I have only ordered from Rima once. Everything went very well and I got my order in a couple of days. Of course, it didn't hurt that I'm in the same metropolitan area that Rima is in...
Anyway, not only did I have a good experience with Rima, but I have read about many people on this and other forums that have had positive things to say about Rima.
Of course, my basic recommendation is for the Ritek discs. Rima was just the place that was cheapest at the time I ordered... There are many other places that sell Ritek discs online and off! As I have no idea where you live, etc, you should definitely use your best judgement to decide what the best place to buy is in your specific case.