I play both BFBC2 and MW2 (don't care for black ops). As to which one I put in depends on what kind of mood I'm in. Both games have their strengths and weaknesses IMO.

I wish I could somehow combine the games into one. Personally, I prefer the mechanics of the MW series. It just has slicker controls IMO. BFBC2 definitely has the edge in just about every other department though. I LOVE the larger maps. I've never been a fan on tiny maps in any shooter (which seem to be the favorites of the MW crowd). And don't even get me started on the Black Ops maps. BFBC2 just has a more mature fan base as well, which is a big plus. Hearing kids that even hit puberty dropping the f-bomb and racial slurs left and right is aggravating as hell (don't think I'd make it without the mute function).

All that being said, I plan on getting both new games. I'm looking more forward for BF3 though