HKS was the softest (drag racing suspension) so I didn't track it too much.
TEIN and JIC were both extremely stiff. However, IMHO the build quality of the TEIN's were better. I have JIC's currently on. I'm thinking about trying Ksports or some of the other el cheapo brands just as a reference.
My JZA70 is a street car with an auto cross background. I will be doing road racing here soon.