Pop,
Flower quality is in the eye of the beholder.
There is something to be said about shape and form, as illustrated by the two pictures. In general, rounder and fuller is better. BUT, you must take into account size, flatness, presentation, and more important in my opinion - vigor, ease of growth, fertility, and fragrance.
I know what you mean by trying to learn what traits are desirable. Looking at these differences can help you make better purchaces. But the bottom line is that it's you that will be growing it. Nobody else knows what you like better than you. Go with gut. Just my two cents.