When I tried the RBC, it was very greasy but also grainy. It didn't have that smooth, porcelein finish that I get with MMF. I use the MMF on cookies since I am also far too lazy to flood and the kids don't like the really hard icing.
I am finding that the key to a good MMF cookie is to roll the fondant very thin. I have made them in the past and didn't take the time to roll the fondant out thin enough and my family complained they were too chewy and they didn't like the texture.
If I am feeling particularly energetic, lol, I use colored chocolates & candy melts as the accents instead of RI. It tastes so much better but it is a pain to keep it at the right consistency so I don't do it often.
I think the best looking decorated sugar cookies are made with either MMF or RI. I think the best tasting is with BC, however, those don't crust, harden up or smooth out enough to look good. *sigh*