What a loaded question. Anyway here goes.
How do you define the class for comparison?
By weight?
By cost?
By engine displacement?

If you are talking power/displacement, then you left off the one that I think would meet or exceed all on your list.....ZDZ. They make the strongest 40cc, 60cc and 80cc singles that I've seen. Soon they'll have a 50cc single to fill out the line.

I think it's better to talk about the merits of a specific size of engine to compare rather than all of a manufacturer's models. As an example, the ZDZ-60 weighs almost as much as the 80, so the 80 whomps it in power/weight.

The manufacturers who use all their own parts (DA, 3W, ZDZ, Moki-Modell, and the future BME) have the advantage of designing their own cylinders, porting, pistons, rod length/stroke ratio, and placement of intake port, method for control (reeds, rotary valve, or piston port). The ones that use industrial cylinders and pistons have to live with whatever compromises were designed into the mass produced engine.