The Japaneese
engines are the best quality IMO ..
Tanaka, Robin Subaru, Mitsu, Honda,
Are the best quality you can get ..
Drive systems IMO the best are GEBE, Staton
Gebe is a Belt Drive
Station has Friction Drive, and Chain Drive... Staton also sell's the NUVINCHI
hub , it's a rear hub that is a CVT..
both are American made ( except engine )
They both offer 2 strokes or 4 strokes.
I would say the Staton Friction drive is the easeyiest install, then the gebe, and then the Staton chain drive..
also note that you really need to get a good quaily rear wheel with the above kits... If you use a cheap wheel you will prob. have to replace it in 6 months... save yourself the headace get a good wheel when you buy your kit.
Good hunting !!!!
Look on youtube they have videos of all these kits in action !!!!! and it's fun !!!