Can someone give me a quick overview of the allegiances of the different heroes lorewise?
Right now it looks like this (to my knowledge):
Overwatch: Winston, Tracer, Torbjörn, Genji, Mercy, McCree, Reinhardt
Talon: Widowmaker, Reaper
Junkers: Junkrat, Roadhog
Helix Security: Pharah
Vishkar Corporation: Symmetra
Korean army: D.Va
Russian army: Zarya
Shimada Clan: Hanzo
Independent: Soldier 76, Lucio, Zenyatta, Bastion, Mei
Reaper and McCree used to be part of the Blackwatch division of Overwatch, Widowmaker is implied to have been the brainwashed wife of an Overwatch agent. Zenyatta used to belong to the Shambali order, Soldier 76 used to be on Overwatch but is now a straight vigilante. Genji was part of the Shimada Clan. Bastion is basically this leftover combat unit from the Omnic war. Mei used to be a member of Overwatch, but once she came out of cryostasis, she became an adventurer on her own.
Also, it's likely Sombra (the upcoming character) will be allied to Reaper.
If you want a breakdown into good/evil it'd be like this:
Evil: Widowmaker, Reaper, Junkrat, Roadhog, sort of Hanzo (the Shimadas are a crime syndicate) and Symmetra (Vishkar is pretty unscrupulous)
Unknown: Bastion
Good: The rest
That said, there's some arguable stuff here (e.g. while Lucio is a freedom fighter, his equipment is stolen), and it depends on the angle of interpretation. Overwatch is illegal, so technically all the people who fight in its name are vigilantes and thus criminals, i.e. evil in the eye of international law, although they do good.