I've never used cornstarch, I have been worried about the taste. Is there an advantage to using cornstarch over powdered sugar for rolling rondant?
I use MMF and used to roll out with PS simply because I was too lazy to remember to buy cornstarch when I was at albertsons. I used it for my last cake and noticed that I was able to get it thinner with less sticking/almost no sticking, and there was no real taste at all. Now if you poured on the corn starch and let it soak in there would be another story....but for rolling out your fondant (for me) it's better
I use a combination of cs and ps (equal parts). I have a small ice cream bucket that I keep it mixed up in so it's ready when I need to refill my "pouncer". I've found that the combination works a lot better than just one or the other.
I prefer the cornstarch because it takes less and it's very easy to wipe off of the fondant once I get it all rolled out.
I use cornstarch most of the time. You need to use very little. But I have tried shortening and it works well too!