Well you can't find a better fight against gamers when you put Battlefield and Call of Duty games in comparision.
For me, I am a single player gamer. I really don't play online except for games like Counter Strike/Left 4 Dead. Hence I chose MW3, because they always had a better single player campaign than Battlefield. But if I was more into multiplayer - I would've chosen BF3 - Which is going to be much, much better than MW3 when multiplayer is concerned
Battlefield 3 features both Single player and Co-op campaign. How is that less than MW3's offer?