There seems to be disagreement about this, but I firmly believe that wider is better for serious snow riding. I have a pair of 26"x1.95" MTB tires that I've found to be great in the snow. They're better than anything else I've tried (although I've never used studded tires.) Ask around, or just get the widest most aggressive tread pattern you can. Better yet, get an old mountain bike if you really want to ride through the white stuff.

*Edit* Here they are: