I generally like MW2 more, Black ops is still fun. Black ops though has cartoonish graphics, if you care about graphics. To be honest I think you should get Black Ops, it has more game modes, it has zombies, etc.
I'd say MW2. Black Ops just has too many problems to merit a purchase. MW2 might have never been patched and it might have some problems, but they're nothing compared to what Treyarch has instituted in Black Ops...
mw2. i have not personally played black ops but i hear much feedback about it from both friends and online communitys, etc. and it seems that the general consensus is that mw2 is better and many players are returning to it.
i played black ops and got bored within the first 6 hours of gameplay because i unlocked everything -_-. The only fun thing on it is wager matches and thats it. MW2 is way better and has way better graphics. Guns might not be balanced but its still a hell of a lot funner than shit ops.
MW2 becaue black ops have lots of try hards with ak47 and cant quickscope. also black ops the graphics are bad. but a pro is less noob tubers, theater and file share(from halo 3),splitscreen, and zombies which is fun.