Edit: Sorry, wrote more than I thought I would. The first and last paragraph sum it up fairly well, if you don't want to read it all.
Personally, I found I had a lot more fun in MW2 than Black Ops, even with all the cheating-level glitches that cropped up. This probably has a lot to do with my style of play; I tend to use single shot weapons, be they semi-auto or bolt action. I like the accuracy of them.
Because of that, I found Black Ops to be annoying as hell. None of the single shot weapons actually make sense. Sure, the M14 and the FAL are kinda powerful, but they're inaccurate as hell. The AK47 has a better overall accuracy than either of them, along with a similar amount of damage per bullet, which makes absolutely no sense in my mind.
Snipers are also broken, and not in the way that makes them all-powerful. Scoping up doesn't put the center of the sight anywhere near the middle of your screen, and you're lucky if you get a one shot kill with any of them (something which doesn't make sense, realistically or balance wise, for most of the snipers). Top that off with maps that are made to cater towards CQC with the occasional medium-range hallway thrown in and you've got a game that really isn't my style.
Another thing that bugged me about the guns is the order you get them in. Generally, the weapons you get later on in the leveling up system are better than those early on. While that makes sense as far as "the longer you play the more we'll reward you" goes, it makes it so that there's little point to prestigeing except to go to the prestige only gametypes (which doesn't really have much appeal to me...). World at War was the same way in my mind, and I never prestiged in that one either.
Combine that with an overall degradation in graphics, single player storyline, and a variety of glitches and flaws that makes it the game's fault that you get screwed over (I literally spawned right in front of an already-thrown tomahawk yesterday, and in between two enemies that were both facing where I spawned) and not the fault of idiots exploiting glitches and I really found it to be a lot more annoying than MW2's multi.
However, the additions are fun. I thoroughly enjoy the wager matches, and the customization you get with face paint, gun colors, emblems and clan tags are all awesome. Also, on the other side, MW2 can be rather sniper heavy at times, and there are some issues with being able to Falcon Punch people from about ten feet away with a knife. There also seem to be a lot more people who using annoying tactics to win (i.e. tactical knife/lightweight combos and noob tubes).
Overall, I'd say it's a matter of personal preference. If you don't mind getting screwed over by the game every once in a while, prefer CQC to long range combat, don't mind working a bit harder to get the "good" guns, and enjoy a more traditionally "balanced" game as far as player-to-player goes, Black Ops is better. However, if you enjoy mid to long range combat as much as CQC, don't mind annoying or "noob" tactics (personally, I always love the feeling I get from headshotting a tactical knifer just as he's about to Falcon Punch me), like maps that are more varied and better designed, and prefer a more balanced progression system, MW2 is better.
