This subject has been debated to practically ad nauseum levels over the years. It's like "which is the best camera" when the actual differences are pretty small.

OS simply has maintained one of the best reputations for quality, ease of handling, performance and value. Thunder Tiger is a Taiwanese clone of the OS when several OS engineers left to form a new company. I have both. The Thunder Tiger will be priced a bit lower than the OS. Some say the OS has the edge in power, others say the TT is the beast. My TT 46 Pro runs very well and has ample power for my applications. Yes, you can buy 3 TT engines for what you'd pay for 2 OS engines.

I don't have enough experience with SuperTigre to be an authoritive source but these are all manufactured in China these days.

As far as 4 strokes, my choice is simple - Saito.