My take is there are a number of teams (NHL, NFL) that would be considered true enemies, though who's #1 would probably vary (Bruins, Leafs, etc.../Dolphins, Jets, etc...). But it would be one-way, as arguably none of those fans would consider the Sabres/Bills to be THEIR #1 rival. Rivals, yes, and even hated at times, but not arch-enemies ala Bruins-Canadiens or Cowboys-Redskins...or Yankees-Red Sox to go the MLB route.
So in Buffalo, you got the Bills and Sabres.
I assume baseball is a bunch of Free Agents between mainly Yankees, Sox, Mets, Jays, and Indians.
Between the Bills and Sabres is there any true rival city or team?
To me the answer seems, no. It's not like Boston really looks to Buffalo as hated....they got New York and Montreal.
Buffalo naturally would seem to hate New York and closer towns like Pittsburgh, Detroit, Ohio, and yet you really don't have any history with those towns, and for some foolish reason you never were placed with other Great Lake cities.
There are definitely tiers to this. Anything Boston usually tops the list, as that city is everything Buffalo wishes it was from sports teams to its metropolitan significance and culture. The Leafs are up there because we share the same market and their fans always fill the arena. Crossing in to Football, the entire AFC East is a safe bet, but it's difficult there because the Bills haven't been relevant enough to really stoke the flames of rivalry.
Philly..... rivals take two to dance, I've spent quite a bit of time in Philly due to family there... no Philly sport fan worth his salt has ever said a good thing about the Sabres or Bills, or Buffalo for that matter. There is a true dislike between the fan bases, they have a long history of distain dating back to the Cup series in '75..