BF3 is obviously more team play oriented. It's great to play with friends as squad up. Winning a game is a lot more rewarding than MW3. MW3 is fast paced and getting a kill is 10x more satisfying. MW3 does feel like more of a patch update to Modern Warfare 2, but still fun.
And btw, is anyone having problems getting into matches and lag spikes? It takes me a good 5-10 minutes to get into a match. Then again, I am playing on PS3, lol