This is what I have: (well, one of many, but the one I use the most)
It's classified as an electric bicycle around here, because it has pedals, tires over 12", and is rated at(no more than) 500-watts. No license or insurance required.
Between the 16", fairly wide tires, full suspension, and the weight of the darn thing, it makes for a comfortable ride. If you don't want to pedal, these are great. You can't really pedal past about 10mph, because of the low gearing.
If you do want to pedal, you need to get something more bicycle like, with gears. But you'll lose out on the wide tires and possible on full suspension as well.
I wish our laws were the same as Arizona...I'd be able to strap a tiny generator on it for backup power!