So much of anyone's answer depends on their personal and riding circumstances. My ten mile commute is on a MUP and over half of those I see while I'm riding are on road bikes, probably closer to 80% today (eight out of ten this moring). When we had warmer weather, I saw a broader mix of bike types. Clearly with the cold, I may be seeing more serious riders. I'm riding what I had, a rigid Raleigh M60, but used a road bike to ride about the same distance on streets in Atlanta 20 years ago. Not many mountain bikes available then and it was what I had. I've only been regularly commuting for three months this time and I don't want to invest in a new bike until I'm sure I will keep at it. Even so, for my commute, I do prefer the more upright position in the MTB. I've ridden the same route on my old road bike and was only one or two minutes faster. This way I keep the bike lights, rack and other weight items on only one bike. However, I've changed my tires to the Kenda Cross Plus with smooth center tread and knobbies on the side. I've just mounted a pair of Schwalbe Marathon Winter studded tires to a spare set of wheels after a couple of days of snow and ice.

Are you riding from Spencer to Bloomington. What's your route and distance?