I've sent a total of three tickets to RTB hosting that were completely related to the server itself, not add-ons or anything I did. None of them have ever been responded to (It's been half a year for two of them). I've been able to contact Kalphiter directly for issues relating to my server on Kaphost, and he has always responded and fixed the issue.
While I like the interface for RTB, I find that a lot of it really doesn't even work. I also can get a better deal from Kaphost (buying in 6 month packages).
I think both services would get about the same rating from me. I've never tried CBM hosting, though.