I think a lot of it depends on how entertaining you think the sport is.
For example, I really like football. I wouldnt call it my favorite sport, but its so entertaining to watch for me that I have about 4-5 teams I casually root for because I watch so much of it, and rooting for a team is alot better than staying neutral. Of course, this all goes out the door when they play the Pats. Whenever the Packers, Titans, or Raiders play I usually hope they win .. just a random thing really and it makes the games more enjoyable.
In Basketball, my 'favorite sport' I have two teams Im die hard for. Celtics obviously and the Kings ( loved that Vlade/Webb/Cristie/Bibby/Peja Era .. still a fan today ) and with League Pass I watch both of them play about 60 or so times a year ( celtics at 7, Kings at 10 .. I dont sleep ). It kind of fun having a powerhouse team ( celtics now, kings in the past ) and a rebuild team ( Kings now, Celtics in the past ) .. nice change of pace from message board to message board.
Baseball is super boring to me unless the Sox are on .. I watch some portion of the sox every night and I love them, but I cant sit there and watch another baseball team play.
Hockey is a little different. Im a big time bruins fan, and I think hockey is entertaining no matter who is playing, but the games arent on TV ( out of market, that is ) so Im forced to watch just the B's because I dont find the hockey league pass worth it.