I neglected to add Meshmixer to my list of suggested 3D modeling software. It's also an Autodesk program and well suited for organic modeling. Those with an artistic bent as opposed to an engineering tilt will find it useful. There are features within Meshmixer that make it worth learning, as an accessory to the more complex previously noted packages. I'm fond of opening a model simply to use the dimensions feature, or to slice with a plane, or run a manifold check.