For me, Superfly was revolutionary. Once I learned how the materials work and optimized them for use in the new render engine, I found that I needed far less light to achieve pleasing results, and using the GPU, renders are far faster than with Firefly. For that reason, I use P12 Superfly exclusively for rendering and animating. I'd kept P11 because of the python script issue -- as a few others here have pointed out -- but mainly for VWD, which is no longer working after a recent video driver update.

I don't know about P13. None of the things I want in the program have been changed. It's still using the antiquated cloth room. I hate most of Poser's hair textures, but can't figure out how to fix them. The new opening page will be useless to me. In my mind, I'm not sure that P13 represents enough of an improvement to justify the expense.