Halo 3 and Call of Duty 4 far surpass Team Fortress, I'm sorry to say. Especially in online play, TF2 falters behind them. It all depends on taste, but those two seem to be the best for online at this point.
I haven't played GTA4, so I can't say anything about it, but I can say that Gears gives the host a ridiculous advantage over the other players.