Well, who are the best fans in Ontario? And what criteria do you use to make the determination?
They aren't just the best hockey fans in Ontario, they're the best in Canada.
The NHL arena in Ottawa is in a horrible location with insufficient transport access. It takes dedication to put up with that commute 40 times per year. Once is bad enough. It's no softy to get to like the ACC or the Bell Centre in Montreal. Ottawa's a city full of Leafs and Habs fans since the team was only reborn in the 90's, and they still manage to cultivate enough Sens fans to get by.
The 67's rink is or at least was a dump a few years ago (not sure if they're part of a Lansdowne makeover). The Bob over in Gatineau is worse. And yet support them they do.
Ottawa doesn't support football (CFL team died, coming back), baseball (Lynx demoted), or lacrosse (NLL team died) particularly well. But no one supports hockey better. They aren't just NHL-only like a Montreal either (which is littered with the dead corpses of CHL teams). One NHL team with a rink in a horrible location and 2 CHL teams that play (or played) in dumps. No other market supports that with 5x less population than Toronto.