Hrm...
Tough choice.
In the end though if you really arn't interested in the 360 exlcusives your going to basically be payign 350 dollars, then a monthly fee just for the ability to play your friends online in games.
Less of a problem if it wasn't developers cutting out local multiplayer, or local online multiplayer. (the one advantage of COD3 over 4.)
Seems like a steep investment just for that.