I've got to say that, while so many guns are overpowered in BlOps, the remove of Stopping Power means that any gun kills in, at most 4 shots so really only accuracy matters to an experienced player. Before I sold my BlOps I tended to reach a 5 killstreak at least once a game and always played for napalm, Blackbird, Chopper Gunner because if you reached them you won; but I still think that the game is fairly balanced due to said bullet damage.
However, Halo gets my vote every time - every gun kills when used right, vehicles can be overpowered but equally can they be obliterated by a well-placed clip of sniper or immobilised with an over-charged plasma pistol. Also, Halo maps have a lot less camping thanks to radar and anyone who complains about Armour Lock has never Armour Locked near relatively unharmed enemies (Armour un-Lock followed by a short flight through the sky).