I do think they are very close. For me the decision came down to the fact that I initially bought a Markins Q20 without a quick-shoe plate, because I wanted the RRS quick-shoe with the lever release, so I figured I might as well get the RRS camera plate to attach to their own quick-shoe. I'm very happy with RRS and you can call them and ask questions and I've found them to be very informative and responsive.
I would say the RRS, Kirk and Wimberley offer the tightest tolerances for Arca-Swiss compatibility, however you can never go wrong with sticking with one brand. I also have the RRS monopod head with their RRS levered QR, and I have my eye on some other RRS products, such as macro rails and flash brackets, so I usually just sit around with the RRS catalog and create my own wish list.
You definitely should wait a little on your decision, to make sure that there aren't any snafus with either product.