If you want 1. A realistic experience and awesome multiplayer, pick BF3. 2.
If you want good multiplayer, brilliant co-op (offline and online), epic single player campaign then pick MW3. BF3's single player campaign is horrid! Personally, I prefer MW3 as it offers the complete package-Good multiplayer, co-op special ops and survival mode is seriously fun especially if you have a second controller so you can play offline with your friend.
However if you are an online only person who prefers more realistic games, pick BF3.
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.