Jeff, Welcome to the forum and we're glad you've joined us here for some fun.
Your questions are common ones often asked by new members or those just getting into the motorized bicycle hobby. Unfortunately there are no good answers. It's sort of like asking "What's better? Ford or Chevy? What you're going to get is opinions and they will be based on the experience of those who reply.
You are correct in that all the kits/engines you see advertised look the same. There is more than one factory that produces the Chinese 2 stroke engines but there is a plethora of assemblers. Basically mom and pop operations who assemble the engines and package them into kits which are then sold by various distributors who ship them.
The biggest differences you'll see are engines which have been modified or otherwise improved by individuals and sold under their brand names. Obviously they will be priced higher than the ebay sellers but they promise quality. Some of them are advertisers on this forum along with those who sell the stock engines and kits. One thing we always stress is to deal with a vendor who has a good reputation of customer support after the sale.
We urge most new members to utilize our 'Search' and you might find a lot of information by typing in the engine name and see what others have had to say, both pro and con regarding that particular brand.
This is an over simplified explanation but I hope it steers you in the right direction.
Good luck with your first build. We're always here if and when you need help or advice.
Tom
