The Mac client for RaidCall is certainly inferior to the Windows client for RaidCall. Most notably:
It's not supported, so there's no guarantee there will be a RaidCall-for-Mac client in, say, eight months or whatever.
Unlike the Windows version, the Mac RaidCall version doesn't retain archives of PM or Members Chat transcripts.
Support for clickable links on the Mac version is limited.
Comparing the Mac versions of RaidCall and C3, though, is a much more subjective question. And here, network effects become relevant: for Mac users, any complaints over the software might be trumped by the fact that all your friends are using that service. In other words, a Mac user might prefer the C3 client to RaidCall's (or vice versa), but find that preference irrelevant if everyone else is using the other service.
Regarding C3: since the /r/Recordings livestream used it regularly, several life-cycles in the software universe have passed. By now, it may well be a much better, more stable client now. And C3 does have one advantage over some competing services: it's free. If memory serves, C3's audio quality is better than RaidCall's, but other services (e.g., TeamSpeak) might have even better audio fidelity.
>It's no longer in beta status, as far as I can see.
From C3's homepage:
>BETA VERSION 0.6.8
Anyway, I have no preference concerning what you all end up choosing. That said, I thought I'd share some of our experience so you might benefit from our experience. Hope this helps!