I’ve been using RME for about 4 years. It just works, works, works. Drivers are robust. Renoise just goes, goes, goes.
I’ve been using them about 6 and my brother even longer. Neither of us has ever had a serious complaint. Would still steer clear of the Fireface units at the moment due to so few computers using a good chipset and less and less even having firewire at all.
(Brother has an original Hammerfall, I have a HDSP9632 in my desktop and plan to get a Multiface 2 and ExpressCard adapter in the future for my laptop.)