Riding a Mountain Bike in the city
I would at least put road tires on your mountain bike - they really improve your efficiency on pavement.

If your commute is urban w/ lots of stops &amp; traffic navigation, the mountain bike handlebar setup can be more maneuverable for tight situations than a road/touring bike. I do miss the maneuverability of my mountain bike since switching to a road bike. A commuter or hybrid bike may be a very good option, with the handlebar &amp; fork designed for more urban situation vs. being tuned for long-haul riding.