I did some research on that exact question and decided to go with RDSport on my E92 when it arrives. I almost posted this exact thread but just ended up searching around instead. From what I read, both setups seem to be quality, but RDSport is considered to be the slightly lower of the two. For me, I like the lower look and most people I read seemed happy with them.
Also tipping the decision in RDSport's favor (for my situation) is that the RDSport factory and HQ is only a few miles from me. Having them do the install is a big plus, especially if/when I add sways and other pieces in the future.
I don't think you can go wrong either way, though, especially when replacing the bumpstops (as I am as well).
I look forward to people with experience chiming in as well.