It sort of depends upon what you are using it for.
Joint compound is meant to go on thin, it is less likely to crack when thin. To avoid cracks use multiple layers. If you are building a diorama, use foam to make a substrate and then cover it with compound.
You can also get "setting type" drywall compound. You mix this with water and it hardens via chemical reaction rather than evaporation. Comes in different drying times and it aways sets faster than pre-mix and cracks less. Its also stronger.
I've used Durhams Water Putty for dioramas and mold masters. Mix with water, doesn't seem to crack if mixed properly and allowed to set properly. Can be cut, drilled, painted, glued. You can find it in just about any hardware or big box in the section where you find putty and plastic wood. I fill vacuform cavities with it. Wont stick to plastic so I have to super-glue the part in after drying.