I've only ridden two RMC's so far but I look forward to riding all of them eventually, especially Medusa.
Goliath: Easily my favorite coaster at SFGAM. The height, speed, and interesting elements always have me laughing the whole time. I think I share everyone's normal complaint re: length though... that extra speed could have led to some great airtime hills if they had maybe down and back the structure one more time.
Twisted Colossus: Unfortunately I never got to experience a duel but the ride was great. I didn't mind the break in the middle of the ride on the 2nd lift like some seem to. For me this one felt a little too much like being on a "bucking bronco" when I rode in the back seat... like everything was constantly pulling me with no sustained segments of heavy g's. The sustained undulation had a weird effect on my enjoyment of the ride in comparison to Goliath and what I see from some of the other RMC designs.