Fat bikes can be fun to ride for short distances, but I prefer other modes of transport in the winter time. Like ski lifts.
I have gone back to steel for both my MTB and my road bike. Neither of those bikes is meant to be raced, just enjoyed for the ride. A Scwhinn Tempo with a 105 gruppo for road riding - plenty quick enough to get me around where I'm going. A Trek 7500 hardtail for MTBing. Both bikes are from the 80s, and both have hand-built (by me) wheels that have served very well.