Federation Commander

For those that sculpt mini's from scratch, do you prefer to use modeling clay or Green Stuff? What do you think is the advantage to using one or the other?

Green stuff.
It's tougher than clay when cured.
It cures completely in air (no baking required)
It doesn't shrink or crack when drying
It's sandable, engravable, and durable
It takes paint well w/o sucking it up like some clays can
It can be used to form castable masters

Indeed. I wouldn't trust modeling clay for anything this small, even for my own gaming table (exuding all "can be cast with" criteria). It's just too brittle, especially when thin and small.

All of my sculpts have been in greenstuff, Tamiya epoxy putties, brass, and steel. Most of my kitbashes were done with "castable" materials.

For the new resin SL2500 minis, I will use styrene and ABS plastic, etc., as it's roughly as strong as the original material and there is no worries about wasting effort that could potentially have gone into a metal-mini mold.