Color and pattern are important, of course, but there are also some things you didn't mention.
Temperament is a big one, for me. I do not consider a defensive, snappy ball python to be high quality, at least not something I want breeding in my collection.
Even more important than ANY of the above is feeding record--a poor feeder is NOT a high-quality animal, no matter what it looks like.
I don't care about the breeder, and I'm not sure I've ever seen a disproportional ball python, at least not within the bounds of normal snake structure.
Obviously health and lack of deformities goes without saying.