Do you follow nfl closely? If you do then the latest Madden games are the best (wait until after superbowl for cheaper price in game etc).
If not pick up Madden 09 because I feel it has the easiest play call selection for beginners.
NCAA is a far better game imo but you can't get it in europe and thus can't play on a pal xbox, but can on ps3.
Have you played Madden 12? There is something called gameflow which automatically picks the best play for you then a coach explains why they have chosen that and how to use that play effectively, If you know what you are doing and want to pick your own plays you can just turn it off,
it's by far the best NFL game by a long shot, It's fun with or without knowledge of the game