For a minute, I was being stoopid, and was thinking BC3 when reading BC2, and was about to say "It's not even out yet..."
Anyways, it highly depends on your preference in play style. The BC2 ultimate edition is out, which includes On-Slaught mode (4-player co-op) and Battlefield 1943 (originally worth 1200 MS points ($15USD)). Sadly, it's the same price (roughly) as Black Ops, but you do get more product than you originally would have.
Black Ops is great too. It's got a much more arcade feel to it, but with larger maps this time around. So, it's something between Medal of Honor/MW2 and BC2, map wise. You get the zombie mode (4-player co-op), Zork, and Dead Ops Arcade on top of the multiplayer.
Oh, and BC2 isn't as much fun if you're playing alone, whereas with Black Ops you can still dominate going solo. Now, if you've got a lot of friends to play with, Black Ops will likely be a ***** when it comes to multiplayer. My friends and I struggle to get more than three of us in a game at once. More often than not the party will get disbanded, and you'll have to retry with your fingers crossed.
So, it really boils down to your preferred playing style. BC2 has larger maps, and longer matches, while feeling a hell of a lot more realistic than Black Ops (by this, I mean it will, at times, feel slow). While Black Ops has shorter matches, smaller maps (though larger than most MW2 maps), and zombies.