This is like asking who is hotter: redheads, brunettes or blondes?
I will tell you that i have seen the RMS alterkation and ridden in an car with the set up and i own, drive and race a big block dart with the HDK setup. I chose the HDK for several reasons: The price point is easier to swallow. The unit is priced well. It also uses some off the shelf components that you can purchase on your own (steering rack, spindles, coilovers). This makes the system cost easy to split up and afford a bit at a time. It is also at a lower cost them some of the competitors. The quality it top notch. The customer service is second to none. I spoke with Denny @ HDK several times in great depth prior to even committing to a purchase. He spoke to me, not at me. He was able to explain his product in easy to understand but technical terms. He also took the time to ask about my build and its intended purpose. I have continued post purchase communication and he is very responsive and has ensured that my expectations were met. In this day and age I think the exceptional customer service is a selling point on its own.