This was my first winter of biking (very limited though, only 5 days between Jan 1 and the end of last week) and due to the (as another poster said it) "normal" winter of much snow, a lack of studded tires or even decent knobbies, and an unwillingness to compete with cars for space on the snowy, icy, slippery roads, I took the shortest route and along the sidewalks (4km each way). However, the roads are wider now, the snow at the edges of the roads is receding with the milder temperatures (and the warmth of the sun) and this week I've been riding on the roads but still the 4km route.
My regular route is 16km each way although, because of cycling goals I wish to achieve, I will do a 27km route on the way home every couple of days, and then there is the "after Friday's work" 60km trip to the camp during the summer months, not exactly a commuting route but better than 4km to the car for the ride to camp.