RPG: Warlock, Ranger, Druid, Rogue usually only in Single player games, where Im gonna have locked containers without a party in a location I cant come back to, because locked containers are an affront to me. If I dont need to be a rogue to pick or bash a lock, then one of the first three. RPG I typically play the "face" of the party as I prioritize charisma, then Constitution, then wisdom, dexterity, and intelligence and strength, it really depends on the game and adventuring party.
FPS: I dont really play often at all since the Military, but I used to enjoy the spy and the Medic in Team Fortress.