The four-stroke 79cc kits are nice, reliable engines and will work well for new riders.
They are limited as far as hot rod parts, but if you want a cruiser, stock is just fine.
There are several wide crank vendors, and most work fine. (Remember you very seldom pedal with an engine anyway)
I get fantastic reliability from my chinadolls, but I know how to speak ringdinger so they love me long time. Most newcomers will have many more problems with the china two stroke kits. Nothing impossible to deal with, but there IS a learning curve that some people NEVER master.
Four strokes are much less owner skill dependant and if all things are equal, will give more reliable ride for noobs.
All that being said, buy a chinadoll too and use the four stroke to run for parts.