[shilala]

The Steelers never have to worry about playing away, they always have a home team advantage. The Steeler Nation swamps every stadium, every game.
Then there's the Packer fans. They shovel out their own stadium, and are fiercely loyal.

I think it's a toss-up between the two, and I can't even think of another fan base that comes close.

I do know soccer fans are completely out of their minds, but stompling people at the gate and killing people in the crowd isn't all that sexy.
Take that away, and someone could make an argument.