If you cannot afford (or have access to) a fat bike, then a 29er with as wide a tire as your frame will accept with mud clearance room (since snow also packs up) will make a very good snow bike.
I went with a friend who have a pugsley to compare, I have schwalbee racing ralph 29x2,4" and even if he has a very small advantage, I've been able to go everywhere he went. I still want a fat bike but I will wait since I don't actually need it.