I can't say which one is best, but I run a Centerforce dual friction clutch. With my combination, I can't complain about it at all. My understanding is that with diaphragm style clutches it's preferred to have the pedal spring removed. I did on mine, no impact on pedal feel/force.
I put a Centerforce Dual Friction clutch in a 70 GTO I had years ago and it worked great but the pedal felt like I was driving a Honda. I got used to it over time.
