In my opinion of playing both games, Id say bfbc2is far better in multiplayer and single. first there is way less hackers playing since punkbuster is almost mandatory to play online, and the single player mode seemed longer, codmw2 was cut to short, and way to many hackers even though leveling up is easier, but this is only my opinion.
lol punkbuster sucks. It kicks normal players more than hackers. UAC2 is the way to go.