Battlefield offers a hard competitive game-play, unlike COD you can even beat the whole enemy team only using your hand-knife.
As I just mentioned, without thinking or team-play only yourself can beat a team out of eight soldiers using nothing but your hand-knife. In BC2 let's look at Squad Rush mode for instance, you need to be very communicative with your team to achieve victory, whenever you spot enemies you must inform your team mates ( And it's even much more fun when on TS / Vent / Mumble. ) to knockout for example four players in a row in BC2 you need to be very skilled to do that, it's not that easy.
Now taking a closer look on BO, or MW2 because I think I speak for the majority when I say it's better. You can always go solo and outgun loads of enemies without having team mates to help you, what's even worst you can pick a handgun with Marathon Pro, Lightweight Pro, and Commando Pro ( If I recall it's name correctly, it's the perk that speeds up your melee. ) then you're almost unstoppable.
There's probably a lot of other stuff that I do like in BC2 more than BO / MW2, so according to the last version of Battlefield and COD, I will definitely vote for BF3.