1)  Zenyatta:  Zenyatta and Symmetra are commonly paired together as they both have unique support abilities that work well together.  Symmetra can provide allies with a little extra overall HP with her Photon Shield while Zenyatta can provide targeted healing.  Their ultimates are diverse in what they do as well.  Zenyatta's ultimate Transcendence provides a powerful healing aura that can be used to make team pushes more successful while Symmetra's Teleporter is used to get dead allies back to the fight faster.  The only real drawback of this setup is that it's a tad weak on the overall healing capabilities that both Zenyatta and Symmetra provide, but their diversities make up for it.

Zenyatta greatly benefits from Symmetra's Photon Shield as it will give him a total of 175 shield HP, which enables him to take more hits from enemies and gives him more shield to regenerate when taking cover to charge up volley orb shots.

Symmetra does benefit from the Harmony Orb, but generally only if she needs healed.  Even though Symmetra usually stays out of harms way, she has poor mobility to seek health packs, but she does have a 100 HP native shield which can keep her healed more consistently on her own.

Zenyatta's poor mobility makes it harder for him to run away from flankers, but Symmetra's Sentry Turrets can help stall offensive flankers in their tracks and can warn Symmetra of incoming attackers, thus allowing you to tell Zenyatta and your allies to watch out for the incoming attackers.

Zenyatta and Symmetra make a great team for taking down tanks such as Reinhardt and Roadhog.  Zenyatta can give these enemies the Discord Orb while Symmetra fires her Photon Orbs at these enemies.  The Orbs can fly through Reinhardt (or Winston's) shields to damage them and all other enemies behind them.

Zenyatta greatly benefits from taking Symmetra's Teleporter when he dies because of his poor mobility to run back to the fight normally.  When Zenyatta uses Transcendence it can allow Symmetra to run in the front lines and attack enemies with her Projector Beam to deal some more serious damage.

2)  Lucio:  Symmetra's Photon Shield pairs well with Lucio in general.  Having all allies have a +25 HP shield gives more HP for Lucio's heal aura to heal up amongst his allies.  Normally shields only regenerate after 3 seconds of not taking damage, but healing effects such as Lucio's heal aura can bypass this and start healing shield HP immediately.

Lucio, having 200 HP, benefits a lot from Symmetra's Photon Shield, as it will simply take more fire power to take him down and decreasing his chance of dying, thus keeping his auras on the battlefield more often.

Symmetra benefits a lot from Lucio's auras.  Symmetra normally has poor mobility, but with speed aura she can dodge enemy ultimates much easier, and allows her to move around faster to put down Sentry Turrets and her ultimate Teleporter.  Speed aura can also help Symmetra deal with flankers more effectively.

Symmetra benefits a lot from Lucio's heal aura as she is usually in range of Lucio to receive his auras.  Heal aura virtually eliminates the need for Symmetra to worry about getting health packs and it will consistently keep her healed up during a match.

Summetra's Teleporter gets less value from Lucio than other heroes since he is the 3rd fastest hero of getting back to the fight faster after dying along with getting other allies faster back as well (thanks to speed aura).  But teleporting Lucio (and allies) back to the fight is still much faster overall.

Lucio's Sound Barrier can protect Symmetra in times when she is getting flanked or enabling her to be more aggressive with her Projector Beam close up to the enemy for a short period of time, which in turn can help charge up Symmetra's Teleporter faster.

3)  Mercy:  Symmetra's Photon Shield compliments Mercy's healing beam very well.  Normally Photon Shields will regenerate after 3 seconds of not taking damage, but Mercy's healing beam (and other allied healing capabilities) can bypass that and start filling that extra shield HP up instantly regardless if the target is taking damage or not.  When Mercy obtains a Photon Shield, it will simply increase her survival by a slight margin, making it a bit safer for her to support enemies in the front lines.

Even though Symmetra usually stays out of harms way and half of her health consists of regenerating shield, she has poor mobility to seek health packs, so she will benefit from Mercy's healing beam occasionally.  Symmetra is generally safe most of the time for Mercy to follow since she typically stays in the backlines with her team lobbing photon orbs or putting up sentry turrets.

Mercy's damage boosting has no effect on Symmetra's Teleporter, but Damage Boosting Symmetra's photon orbs can be very powerful, especially when Symmetra is used to take out Reinhardts, since orbs can penetrate through shields and targets.  Even damage boosting Symmetra when she is up close to enemies with her Projector Beam proves to be quite powerful as well.

Both Mercy and Symmetra's ultimates serve similar functions:  which is to get allies back to the fight faster after dying.  At first you might think that since both are able to achieve this, it makes the synergy between the two less important.  While that is true to some extent, Symmetra's Teleporter still works good with Mercy's Resurrect.  Not every hero will be picked up by Resurrect, including Mercy herself.  This is why Symmetra's Teleporter is still viable along side Mercy's Resurrect.  Having a Teleporter out can also make using Resurrect more responsive, allowing Mercy to Resurrect someone immediately when they have died, instead of waiting until more have died, since the Teleporter will most likely be there to provide the backup.

Mercy greatly benefits from using Symmetra's Teleporter due to her slow mobility to get back to the fight faster after dying and Symmetra can benefit from getting Resurrected, especially if her Teleporter is not out at the current time.  Also keep in mind that Resurrecting someone is still much faster than someone using a Teleporter to get back to the fight after dying.

4)  Ana:  Unfortunately Ana's Biotic Grenades do not increase the recharge rate of shield HP, but Symmetra can still benefit from Ana's Biotic Rifle shots to keep her in the action more often.  Ana's Biotic Grenades can still help her receive more healing in times when she needs it (such as when she is getting flanked).

Symmetra's Photon shield provides some value for Ana is it will allow Ana to withstand some extra damage from getting attacked by offensive flankers.

Ana will greatly benefit from taking Symmetra's Teleporter as it normally takes Ana a long while to run back to the fight due to her poor mobility.

Nano Boosting Symmetra is one of the weaker choices for Ana, but it can allow Symmetra to move into the front lines more efficiently to deal damage with her short range Projector Beam, which will allow her to rev up her ultimate Teleporter faster in return.  But overall, Ana should try to Nano Boost an ally that simply does more damage.

5)  Symmetra:  Two Symmetras are rarely seen together in Overwatch and the main reason is because having two Teleporters out does not really provide much benefit over just one.  It's rare, but sometimes you can do a specific strategy with two Symmetras where you have one Symmetra put her teleporter behind enemy lines so offensive flankers can use that teleporter while the other Symmetra puts her teleporter in a position where all the other allies can go in a different safer area for them.  This will most definitely require proper team communication and planning to make this strategy work good.

Another major drawback of two Symmetras is that you cannot stack multiple Photon Shields on allies.  This is obviously a huge drawback with double Symmetra.

Having twice the Sentry Turrets can be effective, but the enemy can counter this by choosing heroes that can take out Sentry Turrets easily, such as Winston, D.va, Junkrat, Zarya and Pharah.

Overall, I would definitely not bother with two Symmetras if you are an attacker at the beginning of the game or a defender at the end of a game, or even at any point in the game for that matter.  Who knows, maybe I am wrong and there can be uses with multiple teleporters, Sentry Turrets or even Photon Orbs, but I have yet to see this.

1)  Zarya:  Symmetra's Photon Shields offer slight value for Zarya.  Zarya already has a 200 HP innate shield, with Symmetra's +25 Photon Shield, Zarya will have 225 total shield HP.  The little extra shield can help Zarya survive a bit longer, allowing her to be slightly more aggressive in the front lines.

Symmetra is a backline support hero for the most part so she is less of a candidate for Zarya's Projected Barrier, however sometimes Symmetra will come face to face with enemies up close while she deals damage with her Projector Beam.  In these instances, Symmetra can benefit a lot from the Projected Barriers.  Symmetra is a slow moving support hero and she can be prone to getting flanked, so it's usually a good idea for Zarya to keep an eye on her and give her a Projected Barrier when flankers are on her.

Symmetra's Sentry Turrets can be placed in rooms/hallways where health packs are placed, giving Zarya safe access to a health pack when she needs healing if there are no healers nearby.  This could also lure enemies into Symmetra's Turrets as well.

Zarya, being a slow moving tank with no mobility options, dramatically benefits from using Symmetra's Teleporter after dying.

The only thing Symmetra can do with Zarya's ultimate Graviton Surge is to fire a fully charged Photon Orb at the clumped up enemies.  The orb will fly through and damage all enemies stuck in the surge.  It's not overly powerful, but it can do some damage.

2)  Roadhog:  High hitpoint tanks like Roadhog doesn't benefit from Symmetra's Photon Shield as much as squishy heroes do, but the little extra shield can allow Roadhog to withstand some extra damage while he tries to Chain Hook his enemies and giving him some extra time before needing to use Take a Breather (self heal).

Symmetra can place her Sentry Turrets at a choke point enabling Roadhog to have easy slowed targets to use his Chain Hook on if enemies try to make an advancement.

Roadhog's big hotbox can act as a meat shield for Symmetra to get behind to safely fire her Photon Orbs, it's not as effective as Reinhardt's shield or Winston's barrier, but it can provide some protection.

Roadhog's extremely poor mobility makes it very hard for him to get back to the fight faster after dying, so he greatly benefits from using Symmetra's Teleporter to get back to the fight very fast.

Symmetra is almost hopeless when she is being attacked by multiple enemies up close, but Roadhog can use his ultimate Whole Hog to knock enemies away from her or he can Chain Hook one of the enemies away from her.

3)  D.va:  D.va only slightly benefits from Symmetra's Photon Shield.  Photon Shield only provides a +25 HP regenerating shield to D.va's 500 native HP pool, which is not a huge difference for her.  D.va also tends to blow her mech up frequently anyways, so even though Photon Shields do help a little, it's not as useful as it is for more squishy heroes.  When D.va uses her ultimate Self-Destruct she will lose her Photon Shield and Symmetra will have to give her a new one.

Symmetra can place her Sentry Turrets in rooms/hallways potentially protecting health packs.  D.va relies heavily on boosting to health packs and this can make it safer for D.va to boost around the map for healing.  D.va can also intentionally boost into a room filled with Sentry Turrets to lure enemies into the traps.

Symmetra is a relatively slow moving hero with no movement abilities, so if she is getting flanked she has little to defend against it besides using her Projector Beam.  D.va can boost to her rescue and then knock down the flankers by boosting into them.  D.va can then use Defense Matrix to block shots from the flankers and then finish them off with Fusion Cannons up close.

Even though D.va can simply boost back to the fight quickly, she can still take advantage of Symmetra's Teleporter to get back even faster.

D.va can launch a Self-Destruct towards Symmetra if she is overwhelmed by enemies.  At this time, Symmetra can put Sentry Turrets on the ground near her to slow enemies down around her, making it harder for them to run away from the Self-Destruct.

4)  Winston:  Symmetra's Photon Shield gets little use with Winston.  Since Winston has 500 HP, a 25 HP shield is very small in comparison to his actual hitpoints.  Plus Winston can fully heal himself with Primal Rage and can Leap to health packs quite frequently.  Even though, Photon Shields can still slightly help Winston to withstand a little extra damage while he Leaps around close to his enemies.

Symmetra can put her Sentry Turrets in rooms where health packs are placed at.  This can provide Winston a safe place to Leap to once he gets low on health.  This can also lure enemies into her traps as well.

Symmetra's poor mobility and lack of damage mitigation makes Winston's Barrier Projector very valuable for her.  Winston's Barrier Projector allows Symmetra to safely fire her Photon Orbs while taking cover in the shield globe.

Even though Winston can use his Leap to get back to the fight faster after dying, he still takes great advantage of Symmetra's Teleporter to get back to the fight even faster.

Symmetra is very prone to getting flanked and there is little she can do to protect herself (besides her Projector Beam and Sentry Turrets), she can take advantage of Winston's ultimate Primal Rage to bat enemies away from her.

5)  Reinhardt:  Tanks don't benefit from Symmetra's Photon Shield as much as offensive heroes do, but Reinhardt does benefit from it a bit allowing him to withstand some more damage while his shield is down.  Reinhardt frequently lowers his shield to fling Fire Strikes and he tends to take some quick bursts of damage during these times, Photon Shields will simply regenerate the damage up keeping his HP topped off more often.  Reinhardt's shield works great for Symmetra, as it can allow her to safely fire her Photon Orbs at enemies more precisely.

Symmetra's Sentry Turrets can provide protection for Reinhardt by preventing flankers from reaching around through choke points to get behind Reinhardt's shield to do damage to him or allies behind him.

Even though Reinhardt can do a Charge to get back to the fight faster, he still greatly benefits from using Symmetra's Teleporter to get back to the fight a lot faster.

Reinhardt's ultimate Earthshatter can allow Symmetra to have easy targets to fire a Photon Orb at.

1)  Genji:  Symmetra's Photon shield is Genji's best synergistic allied ability.  Being able to have a regenerating shield is huge for Genji and he greatly benefits from having it on him.  Since Genji usually takes a lot of small damage shots while parkouring around the map, Symmetra's Photon Shield helps to keep him alive much longer.

Symmetra can put Sentry Turrets around the map, Genji can use these traps to retreat to if he needs to get to a safe spot to be protected.  Symmetra can put these traps in a room with a health pack to keep enemies away from it while allowing offensive allied flankers like Genji a place to go refill up on health safely.

And of course, Symmetra's Teleporter helps all her allies (including Genji) to get back to the fight faster after dying.  Symmetra can also put her Teleporter behind the enemy so that Genji is already in a flanking position.

2)  Tracer:  Tracer is one of the few heroes that dramatically benefits from having Symmetra's Photon Shield.  By default, Tracer is the squishiest hero in the game with only 150 HP and no innate shields or armor.  The fact that Tracer spontaneously pops in and out of combat, she takes a lot of small bursts of damage.  Photon Shield helps to keep Tracer in the fight longer, increases her survivability and her flanking potential.

Symmetra can put Sentry Turrets around the map, Tracer can use Symmetra's Sentry Turrets to retreat to if she needs to get to a safe spot to be protected.  Symmetra can put these traps in a room with a health pack to keep the enemies away from it while allowing offensive allied flankers like Tracer a place to go refill up on health safely.

Even though Tracer can just Blink back to the fight fairly fast after dying, she can still take advantage of Symmetra's Teleporter to get back to the fight even faster.  Symmetra can also put her Teleporter behind enemy lines so that Tracer is already in a flanking position once teleported.

3)  McCree:  Symmetra's Photon Shield is very beneficial for McCree since it's usually a hassle for McCree to reach health packs due to his poor mobility.  Photon Shields simply help keep McCree in the fight longer.

Symmetra's Sentry Turrets can slow down targets giving McCree an easier time throwing Flashbangs or simply shooting at his enemies in those situations.

McCree greatly benefits from Symmetra's Teleporter due to his slow mobility of getting back to the fight after death.

4)  Reaper:  Symmetra's Photon Shield is extremely useful for Reaper.  Reaper randomly appears and reappears around his enemies occasionally taking small bursts of damage.  The Photon Shield help keeps Reaper healed allowing him to be more aggressive.  Normally, using Shadow Wraith will remove all debuffs (like Zenyatta's Discord Orb), but it will not remove buffs like Photon Shield.

Symmetra can put Sentry Turrets around the map, Reaper can use these traps to retreat to if he needs to get to a safe spot to be protected. Symmetra can put these traps in a room with a health pack to keep the enemies away from it while allowing offensive allied flankers like Reaper a place to go refill up on health safely.

Even though Reaper can use Shadow Wraith and Shadow Step to get back to the fight fairly fast after dying, he can still take advantage of Symmetra's Teleporter to get back to the fight even faster.  Symmetra can also put her Teleporter behind enemy lines so that Reaper is already in a flanking position once teleported.

5)  Torbjorn:  Torbjorn benefits from Symmetra's Photon Shields due to his poor mobility to reach health packs and it can keep Torbjorn alive a bit longer.  Photon Shields compliment Torbjorn's armor pack allowing him to have an overall larger hitpoint pool.

Symmetra also benefits from Torbjorn's Armor Pack, as it can allow her to withstand more damage especially while attacking enemies up close with her Projector Beam.  Armor obtained from armor packs cannot be healed and allies will have to pick up a new armor pack to obtain more armor.

Torbjorn can place his Turret in a position where it can guard Symmetra's Teleporter or Sentry Turrets.  Enemies attacked by Sentry Turrets will be slowed which can give more time for Torbjorn's Turret to output more damage.  This can be a very powerful defense together.

Symmetra's Sentry Turrets can also be placed in rooms/hallways to guard choke points leading up to Torbjorn's Turret to protect it from offensive flankers.

Due to Torbjorn slow mobility he greatly benefits from using Symmetra's Teleporter to get back to the fight faster after dying, especially if he doesn't have his turret out at the time of his death.

If Symmetra is getting flanked, she can go towards Torbjorn's turret for cover.  Torbjorn can further protect Symmetra with his ultimate Molten Core to really scare enemies away from her.

6)  Soldier 76:  Symmetra's Photon Shields helps all her allies by providing more HP that also regenerates after not taking damage.  However, Soldier 76 has Biotic Fields which provides healing for himself and his allies.  Photon Shield is still valuable for Soldier 76, but not as valuable like it is for other offensive attackers.

Since Symmetra is a slow moving hero and has trouble reaching health packs fast enough, she greatly benefits from Soldier 76's Biotic Fields.

Symmetra can put Sentry Turrets in rooms and hallways, Soldier 76 can use these protected rooms by sprinting into them if he needs a safe place to retreat to.  By doing this he could also lure enemies into these rooms to easily take them out.

Symmetra's Teleporter helps her allies to get back to the fight faster after dying, but with Soldier 76, it's negligible since Soldier 76 can Sprint back to the fight fast.  In fact Soldier 76 is one of the fastest heroes of getting back to the fight faster thanks to his Sprint ability, which makes Symmetra's Teleporter not overly powerful with Soldier 76.

7)  Widowmaker:  Widowmaker benefits from Symmetra's Photon Shields as it allows her to withstand bursts of damage while sniping, and it can delay the need for her to grapple to health packs, keeping her in a sniping position more often.

Symmetra's Sentry Turrets can guard choke points leading up to Widowmaker's position, potentially protecting her from offensive flankers.  With this in mind, it's good for Widowmaker to take a mental note where Symmetra puts her Sentry Turrets at so she knows where it's safer to snipe from.  This can also let Widowmaker be more informed where the vulnerabilities to her position is and she can put down her Venom Mine in any other vulnerable areas where the enemy can flank her from.

Even though Widowmaker can grapple back to the fight a tad faster and start firing from long range, she can still take advantage of Symmetra's Teleporter to get back to the fight even faster.

Widowmaker's ultimate Infra-Sight is not overly powerful with Symmetra because her long range weapon (Photon Orbs) fires very slowly and can be hard to land shots on most enemies regardless if they are in view or range.  But Infra-Sight can help Symmetra make more informed decisions on which direction to spam her Photon Orbs at.  Infra-Sight can also warn Symmetra of incoming flankers, giving her enough time to take cover from them.

8)  Mei:  Symmetra's Photon Shields are helpful for all heroes, but Mei can heal herself with Cryo-Freeze which makes having Photon Shield less important than other heroes, but Mei can still benefit from it by allowing her to stay close up with her enemies longer and more safely to allow her to freeze enemies with her freeze blaster.

Freezing enemies up close with either Mei's freeze blaster or Blizzard can give Symmetra easy targets to use her Projector Beam on to help rev up her ultimate.  Symmetra's Photon Orbs travel very slow, so it generally doesn't pair so well with frozen targets.

Symmetra's Sentry turrets slow enemies just like Mei's freeze blaster.  The two combined can make it incredibly hard for an enemy to even move or escape once caught in this combo.  With this in mind, it can be beneficial for Symmetra to spread out her Sentry Turrets so it gives Mei an easy opportunity to "trap" wondering heroes around the battlefield with her freeze gun and Ice Wall.

Mei's Ice Walls can be used to protect Symmetra from offensive flankers by blocking them away from her.  Please note that Symmetra is unable to put her Sentry Turrets on Ice Walls.

Mei has extremely poor mobility (besides using Ice Walls to propel herself to higher areas) so she greatly benefits from Symmetra's Teleporter to get back to the fight faster.

Mei's Blizzard can make it safer for Symmetra to go up close to use her Projector Beam to easily take out the chilled/frozen victims.

9)  Junkrat:  Junkrat tends to take some quick burst damage as he peeks within view to lob his grenades, Photon Shields can keep him healed up better allowing him to not worry about health packs as much.

Even though Junkrat can use Mine jumps to get back to the fight faster after dying, he still greatly benefits from using Symmetra's ultimate Teleporter to get back to the fight quickly.  Symmetra usually places her Teleporter in a position where Junkrat can immediately start spamming his grenades once he teleports in.

Junkrat can place his Steel Traps in places to guard Symmetra's Teleporter from getting flanked.  Junkrat can also use the Trap/Mine combo to make his defense even stronger.  Symmetra can also use her Sentry Turrets to further protect her teleporter from enemies ambushing it.  Sentry Turrets in general can also help protect Junkrat's position from flankers.

10)  Pharah:  Photon Shields from Symmetra can help Pharah survive a bit longer and allowing her to stay more aggressive and not worry as much about obtaining health packs.

Pharah can lure enemies into Symmetra's Sentry Turrets by flying in the air and shooting rockets down below.  The enemies will try to take cover from her rockets by going inside somewhere such as a room filled with Symmetra's Sentry Turrets.

And of course Symmetra's Teleporter will enable Pharah to get back to the fight faster after dying even though her Jet Packs can help her get back to the fight normally somewhat quick.

11)  Hanzo:  Symmetra's Photon Shield is very beneficial for Hanzo since it's usually a hassle for Hanzo to reach health packs due to his poor mobility.  Photon Shields simply help keep Hanzo in the fight longer.

Symmetra's Sentry Turrets can slow down targets giving Hanzo an easier time lining up Scatter Arrow shots or simply shooting at his enemies in those situations.  Sentry Turrets can also guard choke points leading to Hanzo's position, Symmetra can then warn Hanzo of incoming attackers coming his way.

Hanzo greatly benefits from Symmetra's Teleporter due to his slow mobility of getting back to the fight after death.

Hanzo's Sonic Arrow can help Symmetra start firing Photon Orbs even before enemies come within view of her.  Normally Photon Orbs travel very slowly, but when combined with Sonic Arrow it greatly enhances the accuracy of hitting something coming around a corner.

12)  Bastion:  Symmetra's Photon Shields helps all her allies by providing more HP that also regenerates after not taking damage.  However, Bastion has a Self-Repair which provides healing for himself.  Photon Shield is still valuable for Bastion, but not as valuable like it is for other offensive attackers.

Symmetra's Sentry Turrets can protect choke points leading up to a Bastion Sentry to further protect him from offensive flankers.

Symmetra's Teleporter is very beneficial for Bastion to use since he is slow moving and normally takes a long time to get back to the fight after dying.  Getting Bastion's high DPS gatling gun back in the action ASAP is extremely beneficial.