The Rabbitohs club has to have the best supporters. Though they are based in Sydney, the team actually travels to Perth once or twice a year, to put on a game for their many loyal Western Australian supporters. What other club would travel so far to their fans?
I agree that the Rabbitohs have the best supporters. They constantly show how loyal they are (with membership numbers and their refusal to let the team be kicked out of the competition permanently) and you would never avoid going to a game when your team is versing Souths (because you're concerned about the reactions of the fans if they lose, which applies to some other clubs).