Depends what you are looking for in a team. When I was about 15 and started watching NFL and playing Madden, I picked the Giants because they play in glorious blue and white (and their rating on Madden was ok too). It's a good team to pick now because they have 2 Brits playing for them.
If you want to support a dirty team, go for the Steelers/Ravens/Raiders.
If you want to support a rubbish team, so its just like following Latics, go Rams/Raiders/Browns/Lions.
Saints are good to watch.
But if I was to get into it now and had to pick a team, I'd prob go for the Packers. I like the way its just a small town with a big NFL team, and loads of history.
Don't go for the Cowboys/Patriots....people will end up disliking you! Oh and the Buccs, cos they are owned by the guys who own United.