I agree; Turbos are king if this is a power-only contest. Most efficient and lowest cost if you can fabricate and have room for the hot-side plumbing.
However...belt driven turbos (centrifugal superchargers) are a close second and my personal favorite. Why?
- You lose 2/3rds of the plumbing/fabricating requirement, especially the hot-side which can be especially problematic because it must be kept from wiring, plumbing, paint, etc.
-Centrifugals aren't as efficient because they take crank power to drive, but give some of that back in discharge temperature. The air they discharge isn't as hot because they don't spin as fast. Often times this means you don't need an intercooler.
- The boost-vs-rpm relationship is predictable and repeatable with the centrifugal blower. With a turbocharger, just how much boost you make at a specific rpm has to do with a lot more than engine rpm and can change depending on how the vehicle is being driven. This makes it harder to tune...especially on pump gas. Do you make 3psi or 15psi at 2000RPM? That depends on what you did to get there. Not so with a centrifugal...it's always the same head pressure versus rpm.
- Reliability. Assuming you aren't over-spinning a centrifugal supercharger and are using a well engineered brand, they last damn near forever. Turbos need maintenance. I'm not saying they're unreliable, but in my experience they need far more care than a centrifugal. Turbo-timers to keep them from coking bearings, seal replacements, cracked exhaust housings...etc.
The largest reason I didn't go turbo on my Cobra is because of the plumbing. It created a fabrication nightmare that would required more effort than I was willing to dish out. The concept sketches with the supercharger were twice as clean. And, honestly, the turbo only offered me more power and more heat...which was the last thing I need in this car. 500hp in a street Cobra is scary; 800-1000 is suicidal. Give me a turbo and I'd have died the test drive.