I'm starting to like riding on big fat knobby tires...kind of slow, but I'm not really in a hurry at this stage. Plus you can leave the pavement for stretches when necessary. I only started using my MTB because the rest of the fleet was unfit for action for various reasons, but it's actually quite a bit of fun. I'll probably want to ramp it up a bit as the body rediscovers sustained high level effort, but hopefully by then I won't feel like a total ass on a fast road bike.