I ride my mountain bike when I commute. It's a bare-bones Giant Upland, and maintenance is easy (tires are easy to change, etc.) so I don't worry as much about a mechanical problem causing me to be late to work. It also handles well in traffic, not that I have much of that to worry about.

My route is in the city, but it stays close to the river in a quiet neighborhood. It's about a 4 mile ride - very pleasant. I love it! Destination isn't in the best neighborhood, but I skirt around the far end of parts that make me nervous.

Deb