*Now, before you start ranting and raving about how Christian Lander is terrible and how I'm completely unoriginal, just know that both of us grew up in the same city, went to the same university, and knew practically the same white people. So I would have come up with this idea anyway...it was just a matter of time. And yes, he's terrible. I won't do this often, I promise.
Number 1: England
North American Football Fans or NAFFs usually first got into the game through internationals, and their team of choice is invariably England. To a non-NAFF, this might seem a little odd; England have only won one rigged tournament well over forty years ago, and haven't really done much since. Why wouldn't NAFFs support the USA, or the Canada (NB: 'North America' in this instance refers its modern usage i.e. not including Mexico)?
England provides several key advantage to the NAFF: it doens't win much, so followers cannot be accused of 'glory-hunting' (pretty much social death to the NAFF), it is European and therefore more 'authentic,' and England is home to the Premier League, the NAFF league of choice. Plus, English supporters sing tunes you know with words you can understand (eg. "Two World Wars, One World Cup"). The topper is you don't have to buy an England jersey; you can use the one your uncle gave you in the late 1990s, pretty much the golden age of soccer to the NAFF.
Most regular NAFFs, not having personally experienced drunk xenophobic England supporters abroad, support England unconditionally. Recently however, some super-NAFFs have begun to criticise England in step with actual English England supporters.
WARNING: Do not say David Beckham is your favourite England player to a NAFF -- it would be best so say, "Wes Brown's form seems inconsistent this year," or "Joe Cole is the most underrated winger in the sqaud."