Single player - CoD4 Multiplayer - Battlefield 3 Multiplayer with CoD4 is filled with people with infectable menus (Not hackers, well there's some) and you won't have that much fun. Never played Battlefield 3 though. I love multiplayer and could care less about Single player on FPS games.
Got a total of 10 seconds in Single player on MW3 from accidentally clicking it.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.