On my Schwinn Typhoon 2-speed, I like to ride fast enough to make the tires sing but slow enough that wind noise doesn't drown it out. That's a very narrow band and I'd guess about 9 mph.

On my commuter (3-speed Schwinn Continental with very upright seating) I probably cruise around 13 mph.

On my RANS V-Rex if I'm neither loafing nor pushing it's around 17 mph.

On my unicycle (24 inch), somewhat faster than a walking pace but not quite a run.