In my view a 50cc bike is useless, i own a Honda Metropolitan and its super slow. If i would definitely choose the 125cc scooter or motorcycle. The Zuma 125 and the Grom 125 are priced about the same, although getting a Grom at MSRP is difficult but not impossible. Zuma has a CVT transmission, great for the city and easy to ride, the downside its difficult to modify the final gear ratio, not impossible but expensive, and unable to use lower gear ratios when attacking hills. The Grom has 4 gears to choose from, changing the final gear ration is easy, as it only requires new sprockets and a hour of work.
The Grom top speed is 65mph with stock final gear ratio, its drag limited.
A friend of my owns one, he loves it, he has even gone to LA area and back, he lives in the county of Santa Cruz in California. He has a fuel log here, his bikes name is Morg. I also believe the Grom has the same engine as the one used in the European Velomobile that attains 217mpg, it uses the Honda Innova 125i scooter.
http://ecomodder.com/forum/showthrea...diy-11970.html
Gil