I originally was going to get a Supercard (mainly because it's GUI is awesome) then of course I started reading most people's accounts of theirs and it's compatibility. It still looks like a good card and with the updated firmware it looks like most of the problems were ironed out and I know any still there would probably disappear over the next few updates. R4 is a bit cheaper from different retailers and according to it's most recent review, it's 100% compatible right now. You're not gonna get the pretty GUI that SC has, if that matters to you at all. Didn't matter all that much to me because I'm supposed to playing a game, not looking at pretty windows
And hopefully, more customization of the R4 will come with updates. I guess it's all really what's most important to you and what's most convenient.