I only got MW2 because it waws a quick online deal for $50. I got Uncharted 2 the next day for 40! I priced match with Wal-mart for $50 and got someone who works there to get me another 20% off, so 40 bucks. Though I would gladly pay $60.
For multiplayer, I think it comes down to personal preferance, but I think most would agree MW2 is slightly better in that regard. Of course, there's no reason you can't play both. On the other hand, I think you'd be hard pressed to fing someone who likes MW2's single player better than UC2. The story in that game was very weak. It was just a string of "moments"(even if they were pretty damn awesome). Uncharted's "moments" on the other hand, not only have a good story and the best characters and voice acting in any game ever to try them together, but the "moments" aren't just for show. They are part of the gameplay. The building collapsing, the train, and the convoy all come to mind as the best of the bunch.
*MW2 spoiler alert*
But I'm not trying to say MW2's single player sucks, just its story does. The blackout in DC during the massive storm made my jar hit the floor. The airport scene and the bungie jump followed by a stab to the heart were shocking. And the ending was incredible as well, but I won't spoil that.
In the end, play both!
Now my words, are frosted with every breath
Still the hate burns wild, growing inside this heart
When the wind changes course when the star align
I will reach out to you and leave this all behind
When Heavens Divide