I use straight gumpaste (Nic Lodge’s recipe) when I want something sturdy or fast drying. Such a plaques or a base for a cake topper. Or for heavier petal flowers such as Magnolia. Fondant with Tylose powder added works quite well for things with some motion to them, such as the Fall leaves you mentioned. Straight fondant is too soft for flowers or leaves and 50/50 is alright. You just need to experiment with small pieces of any of those, roll them out and let them dry. Then see which dries fastest, which seems most fragile and breaks easily, which you can roll very thin without it shrinking back after it is rolled. I know many flower makers prefer something like Platinum Paste or if they plan on keeping the flowers for years you might try Cold Porceline paste. Hope some of this helps.
Shirley
