Here in WV I think it's (NFL only): 1. Steelers 2. Browns 3. Dolphins - Believe it or not, there are lots of Dolfans here. 4. Ravens 5. Redskins 6. Bengals - they are coming out some this year again.
I think there's more Dolphin fans in the Boston area than any team not named the Patriots, and I don't think its all that close. I would agree that the Giants are 3rd on the list (but these are mainly older-generation Patriot fans who developed a soft spot for the Giants after watching them growing up -- the Giants were the only team broadcasted in this area back before the Patriots were in New England). After those three teams, the amount of other fans isn't significant enough to really judge. Of course, Boston has always been (and always will be) a baseball town. So if we're talking all sports then you can slide the Red Sox into the #'s 1-20 slots followed by the Patriots, Celtics and Bruins.