Can you even watch NFL games in Belgium?
The Ravens of course! And I'm sure the other Matt will say the Eagles.
If you don't want to be a douchebag bandwagon jumper then you don't want to root for the Patriots or Colts. I'd say a good team to root for is the Green Bay Packers. They're one of the most talented teams in the league and came into this year as a Super Bowl favorite, but they've underachieved a little and they'll be lucky to make the playoffs. I find the Falcons and Saints easy to root for too, but the Falcons have the best record in football (although I think they're a little overrated) and the Saints won it all last year, so neither meets your criteria.
I actually think the Lions are on the rise. They already had one of the best wide receivers in the league, and through the draft they've added a beast of a defensive tackle, a good tight end, and a top-pick quarterback (although he can't stay healthy). They're getting some pieces together.