For me, the best option is to make my own. I make Michelle Foster's Fondant, it is the best! Upfront, the ingredients are a bit costly (glycerine, corn syrup, gelatin e.t.c.) but in the long run it is far cheaper to make your own and you will always have it on hand. It also takes a bit of practice to get it to the right consistency.
I love the taste of marshmallow fondant, but it is a sticky mess to make, so I avoid it! It takes a long time to clean it up.
I tried Fondx and thought it smelled and tasted like chemicals.