I've played TF2 far less than I've played MW2, so I can't properly judge it. I like the "feel" of the MW2 weapons, and I'm accustomed to keeping track of various enemy killstreak and loadout choices. You make your own classes and the differences in the role you play are much more vague, so it doesn't feel like you have to step into a specific character, something TF2's voices don't help me with.
Then again, this is judging from 8 hours of TF2 versus 135 hours of MW2.
In the end, it's a matter of which game you enjoy, not of which game is "better". It's all opinion.