I like the slower speeds of MTB's, I know I'm safer and can go places not practical on a racer, like up and down gutters and along footpaths to avoid busy intersections. I never resent having to slow down or stop either, it's just a good excuse to speed up again. I also know if I was on a bike that could cruse 10MPH faster I would get used to that speed and would be right back where I started but with less margin of safety.