I wanted to give 3D sculpting a try, so I found an open source program called Sculptgl. It has both a browser based app and a stand-alone app.
I found the app easy to learn and fun to use. My first project was a beholder from Dungeons and Dragons, which I then printed in black on an Ultimaker 2plus. After, I primed it in white, splashed it with shade, and then painted it.
I think it turned out great!