Here's a fun thing: I bought both MW games, and went back to Gamestop to pick up something new. I ended up getting the first BC really cheap, as a recomendation from one of the staff.
I got home, and I breezed through the first game. Not that it was short, I just played it mostly in one sitting because it was so damn fun! The very next day, I went back to Gamestop and got BC2, and wouldn't you know it, it's even better.
As I statted elsewhere, I don't think there's any reason to compete both games against each other. I see the two series as being two companion pieces, both pretty good, both worth playing.