I'm not sure there's an official, definitive way to differentiate a devout fanbase from one that's not nearly as collectively loyal. Every fan thinks their fellow fans are the best fans so it's pretty obvious why I consider the Who Dat Nation to be the most impassioned group of supporters that exist in sports.
Well, that....and the fact that some of the more outgoing, optimistic members apparently had premeditated, illegal acts of pettiness planned far enough in advance to have explosives handy at the notice of thee moment that was unequivocally the most catastrophic to their fiercest rival's entire franchise. I'm pretty sure the Presidential election that just passed made us all a little bit dumber, but if it taught us anything it's that you can't just judge a person's level of allegiance by how much they defend something or someone. It's not until you see how feverishly they blindly hate the something or someone that goes in direct opposition of their rooting interest that you can really take the pulse of just how devoted they are. The city of New Orleans getting their Yosemite Sam on and turning a late Sunday night in early February into a 4th of July-esque celebration of the Atlanta Falcons failures may not be proof positive that they have the "best" fans, but I'll be damned it ain't evidence that they some of the most spiteful, proactive ones!