IMO Mw3 looks terrible. It's the same guns, same type of story, same GFX every single time. Also with the loss of a lot of key developers when activision signed Infinity ward, the game will suffer. You also forgot to mention that you will have to pay $10 more a month on XBL if you want certain features. It's rather ludicrous as they are basically taking advantage of their young fanbase (because mostly 12-14 year olds play it) who will beg their parents to pay the extra 10 a month.
Battlefield 3 should, and IMO will beat Mw3 this time. The graphics look amazing, the gameplay is different and inviting, and it's just a better game. It offers the same things as Mw3 but without the $10 stipend.