Im not gonna read it all, but if the SR20 was so amazing, Nissan would have put it into a GTR.

The reason why most people do an SR is because of the price, the availability, and the massive amount of parts support. Thats it. Its EASY to make 300whp out of an SR. Its a good reliable motor that is CHEAP and easy to install.

KA- Not a bad motor, but has to be built, hard to find with good mileage, etc
RB- Technically the 25 and 26 are VASTLY superior to the SR20 IMO, but its a much more involved swap to put those motors into S chassis. Much more expensive as well. Id rather have a SR20 over an RB20 personally as well. I think the RB20 belongs at the bottom of a river.

RB25 is my personal favorite because its a good balance between HP/Liter/Parts selection and cost. But thats just me.