If what rebel is saying is true (which I don't know), and you want to play online, it might be better to just wait for carbon and get that. Though it's pretty crappy if EA really would do that again, most wanted hasn't even been out all that long.
As for which is better, it really is a matter of taste... I prefer MW over U2, the cop chases are fun, and in my opinion it works a lot better with my steering wheel which improves my enjoyment of the game a lot. I liked the mountain roads in U2 though which are gone in MW, but something similar should be back in carbon again.