Bf3 > mw3
I haven't played MW3 but BF3 is pretty fun and will be hard to beat.
You got a copy that worked? I had it freeze up during the campaign and it only counted the first 45 minutes of play on MP. I really wanted to like it, but it's like the '70 Cougar I used to own. It got a lot of compliments for the way it looked, but it ran like crap most of the time. MW3 actually plays as advertised on the first night straight out of box.
I haven't had any problems with my copy.
I have not had any problems whatsoever with it except for getting owned for not buying the game when it came out. I had to build up my weapons to the level of others to really start competing.
My main complaint on BF3 is the sniping is messed up with flashlight-bright reflective scopes and what looks to be tracer rounds shot out of my rifles.
I agree about the flash of the scopes. However, I do think its cool that BF3 actually uses ballistics on their rifles. For example, if you're a sniper and you're making a long shot, you have to worry about bullet drop. I was playing one night and had a long shot and had to use the 2-3 mil dot to make the shot! On top of that, if you have a suppressor it affects bullet drop ever more. Kind of cool, they added some real world physics to it. Plus the destructive environment is nice. You can use a tank to blow a hole in a side of the building where a sniper is hiding.