Re: Which engine is best??
There is a difference in what you do between unboxing the motor and installing it in your bike, however.
If you take the time to port match the intake, exhaust, jug you will see an improvement. Swap out fasteners as you go. Slap on a Puch head for an added bump in performance and cooling. One thing I found is that the covers on the side of the engine had a lot of flash and did not sit square on the case. If you sand the mating surfaces flat, you risk less leaks and vibration. Also, use loctite and anti-seize where appropriate.
So really, there is more that you can do at home to help than just picking a factory over in China.
I would rath buy from one of the big names so that I know that support and replacement parts are easily found.