Sculpting 3D models is my favorite. It helps with understanding the anatomy of whatever you are working on. I can sculpt a small section of whatever I'm working on with as much detail as my imagination can take me. Once I'm done, I can imagine that section vividly and be able to draw it, paint it, know how it moves, and know how it grows through time. It's a great way to get to know your subject. All other process of creating a 3D characters have their own spark, but sculpting is my favorite.