Here is what I have been able to gather from researching this same subject:
Both have great coils. Both have a solid reputation for quality. The plush ride springs (Evo) are the best overall coil for road comfort although both Evo and RK coils are great on trail.
Both have solid customer service.

Here is the thing that may have helped me to decide. Every question asked of an Evo rep on this forum has been answered in a timely fashion. I PMed the RK rep directly and he did not answer my questions. In all fairness this is opposite of the standard experience, but their rep left me hanging after a direct question.