It kinda sorta depends what criteria you're looking for for your rankings. In the case of Dallas, or the Steelers for that matter, there certainly are a large number of fans, anyway. I don't think that should be the measure, though. I'm partial to the fans of downtrodden organizations who still show up enthusiastically after years of disappointment. Cleveland, maybe, or Kansas City would seem to be pretty good examples. Saints fans are a great example, though that team is good right now. They were awful for years and still had people dancing in the streets.