I've felt all but the Princess (which you probably won't be needing anyway). The granite and champagne covers (for the 65s) are like the pp said...kind of a microsuede feel. They're soft, but not super squishy. The covers that come on the 80 are a bit more squishy. I didn't like the Super Cool either. I'm not a fan of mesh, though. Maybe if I were in AZ or something, but I don't see the point otherwise. The other covers (Manhattan, Monaco (and the Princess, I believe)) are all the more plush-feeling covers. Kind of a soft, fuzzy feel. And to me, it seems like they're just a bit more padded than the 65 covers. I don't know that I'd pay that much more just for the cover, though.
If you're going to get a Radian XT, though, I have no idea what material those are. But I can't wait to see one IRL and find out!