Here it is again, the "We're your rivals too!!!!!" mentality.
Most? Stony Brook. Had two full sections. For hockey, of the two, probably BC consistently. Most in general, Maine, not even close. There were close to 1,000 Maine fans at Agganis in November.
But how ever many fans the opposing team brings isn't a sign of a rivalry, especially if the home team's fans don't show up, as is the case with many BU-NU games at Agganis. Northeastern is not a ticket seller for BU the way BC, Maine, UNH, and a big time OOC game (Michigan, Cornell, Minnesota, etc.) You can expect those games to be drawing 6K to a sellout pretty much every time. If an NU game draws 6K people to Agganis, that's a sign something is up, and it's only happened once recently, in February of 2009.
Another example of what I'm talking about. "Yeah, BC-BU is big, but so can we!!!!"
If you ask an average BU fan to list who they consider are the top rivals of the program, you won't see NU listed in the top five of most people who actually pay attention to the team consistently. As eric said, BC's always going to be number one, and the gap after that is huge, then you'll see a smattering of Maine, UNH, Cornell, especially with the MSG games, heck some old timers might throw in some more ECAC teams like RPI and Harvard, but after that top tier of BC, UNH, Maine, and Cornell is where you'll find NU. That's the way it is. I know you all go ga ga every time we play, and we're supposed to be your biggest rivals, but the feeling is not reciprocal, and over the course of the season, NU is not a game BU fans mark on their calendar, that students line up for, and that tickets are hard to come by on game day. This is a one-sided rivalry except for the infrequent meaningful game the two play.