Well, my Thalia in the Mines vs. the Thalia WIP is an interesting one, as the WIP has a pretty female face, the final has a clip from the monster. My Indigo in the Catacombs uses a much brighter thumbnail because otherwise the render is too dark to make for a good thumb. I've tried a number of things, but I seem to be getting good responses (except for my latest render -- I need a better choice of lights for it).