I dont know b=much about them other than everybody loves the ruckus. talk to mistahT he has/had a few
I've had a bunch of scooters (well, and my friends don't have garages, so they kept their scooters with me. For a while I would work on and ride them all pretty much whenever I wanted

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For reliability and longevity, stay away from cheap chinese scooters. Had a few, 1 never broke down, but the rest were constantly in need of repair.
2 stroke and 4 stroke Zuma are both nice bikes and, surprisingly, the newer 50cc 4 strokes are supposed to be the same speed as the 2.
The Ruckus is a really cool bike. You name it, I've done it to my bike or someone else's. Stretched way out, huge rear tire, 150cc motor swap, etc. I used to get rolling high-fives from strangers and people hanging out of moving cars to ask what it was and tell me how cool it was. You can make or buy just about anything you can think of for it. And if you play your cards right, you can do a 150cc swap for under a grand like I did.
Down sides: Might want to look into upgraded suspension first being on the bigger/heavier side. Also, Rucks are not terribly cheap and get stolen a bunch. My buddy just got his jacked last week and now has to take the bus. Unlike the Zuma, there is ZERO storage space on the Ruckus.
Don't be disillusioned by the 50cc. They are great fun and great on gas, but sloooooooooooow. the 35-40mph top speed doesn't get you as much as the complete lack of acceleration. 150cc swap is fun, especially blasting by cars at nearly 65mph, but these can be illegal and the motors aren't as reliable as the stock honda. (In my own experience, I never had an issue with my 150cc engine, but the stock carbs for it were another issue :banghead

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I loved my Ruckus and still miss it sometimes, but it's nothing like a motorcycle. Real moto better in everyway.