For synthetic modeling I use Electric Image Universe, which has a great set of tools. I seldom plan out my models, usually I have an idea in my head, and just uses the various tools to create it. Sometimes I will use an object in front of me or guide images loaded in the modeling windows. For organic I usually use Amorphium ( now at version 3 ). Some of my best stuff is spontaneous. I just start doodling and get a shape then go from there.

I have done planed out modeling, in both apps, I just find the spontaneous work more fun

Stephen Ray