In the winter I normally ride a standard mountain bike with studded tires. The tires have a huge amount of resistance and really slow me down, so I don't enjoy riding that bike when it's not icy enough to justify it. As soon as the pavement is clear of ice, I'm back on my regular hybrid commuter with 32mm tires until the next snowfall.
Fat bikes seem to be all the rage right now, and admittedly they look pretty cool. However whenever I see one coming I can hear the whir of the tires from 50 yards away and I can't help but think how much effort is involved in riding those things. I could see how it might be fun to take one on an occasional spin, but I don't see myself wanting to ride one day in and out for my regular commute.
I guess I'm just lazy.