From my experience ,both thin and fat tires have their uses for winter commuting. It all depends how much snow and what type of snow you are riding through. Both thin and fat tires will have their advantages and disadvantages. The best thing to do is to try out and test different types of tires under different conditions and see how each tire performs. Some people can get through the winter on 28mm tires and others are
riding 3 inch tires, to each his own. I ride both fat and thin, but if I only had to have one size I would choose something around 38-40 mm.