Personally I dislike BF games. I got Battlefield 2 complete, and BFBC2 but it was kinda buggy and has too less weapons for my taste.

MW2 was my first CoD game, I bought rest of them (MW1 and older) from Steam sale once as a pack. I got BO as x-mas present, but didn't like it very much... Have played MW2 100+ hours, BO less than 30 hours (because I don't like it very much), and a little bit those older ones.