Fondant and sugar paste are usually the same thing. They take longer to harden than using gumpaste, or a mixture of gumpaste. For some things it wouldn't matter, but for bigger pieces they could distort as they are drying if it takes a while.
Marzapan is made from almond paste. I haven't worked with it. I'd think it'd be the more expensive of the three to use, but if you were going for a figure that someone would actually want to eat, then I think it'd be the one to use.
I have almost always used fondant mixed with gum-tex or tylose or gumpaste when making 3d figures. I like making them 'edible' but no one really eats them.
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