I've commuted on road bikes like a Cannondale R400 and a Redline 925, I've also commuted on mountain bikes full suspension, and on singlespeed mountain bikes like a Monocog. Road bikes are much faster. I've had my 925 up recently to 27 mph. The most I can get out of mountain bikes is 21 - 22 with slicks on the tires. I have one of my Redline Monocogs set up with studded tires. When the road starts thawing in the springtime or late winter, I use my full suspension mountain bike to absorb all the potholes on the way to work. I don't have the Cannondale R400 anymore, it was the fastest bike I had. I could get that bike up to almost 40 mph. But I found out that I prefer singlespeed bikes for the pure fun of it. Have a good night.