Organize you're GameQ better. Maybe only 1 xbox game is available and the next one is a PS3 game. When you're expecting some of you're games to be shipped organize it and make sure that 1 PS3 and 1 xbox game is available.
It comes down to a personal preference. If you like a more fast paced arcade-ish game then MW3 would be the one you would want. If you like a more realistic objective based game with vehicles and big maps BF3 would be the way to go. If anything rent one if you don't like it just switch it out.