Black Ops seems to have many problems with online, like spawning problems, or how some weapons are overpowered , unlike Modern Warfare 2, where most weapons were equal, just with different advantages/disadvantages.
Black Ops did, however, have an amazing campaign, and zombies is alot of fun. Not to mention, there were many secrets throughout the game.
Overall, I can conclude that MW2 > Black Ops with multiplayer, but with campaign and co-op (Spec Ops and Zombies being the co-op modes) it's probably safe to say Black Op > MW2. If you look to your right there is a poll. Vote, and post why in the comments below.