I usually have one favorite at a time and stick to that one because, as a person of limited resources, I want to make sure that I am guaranteed to get the best value (of what I like) for my hobby dollar.
In a recent meeting with my favorite, we were talking about two other girls I had met who work for the same agency that I met several days apart.
"The first one," I said, "had great physical skills but terrible interpersonal skills. The second had great interpersonal skills but, physically, was just not cutting it. That's why I keep coming back to you, because you are the full package."
So that's what I look for in a favorite: The full package.
That, to me, includes beauty, intelligence, great conversation, great attitude, healthy sexual appetite and an eagerness to please (very similar to Randolph's list above).