Loki, I fall under #4.
As for your experience with your provider, it could be a combination of both. First off, repeating with her could increase her comfort level with you. Making the experience more enjoyable for both. Secondly, if she's a really good provider, she will be observant as to what you like and dislike. A good lover will do that, and THAT will make the experiences even better.
The logic of find the best and keep her would be very difficult to actually do. Think about it, you'd have to see every provider in the city, and then decide. Unless you have the time and cash, that's going to be pretty well and impossibility.
You can stick with your one sp and 1) things could end up getting better and better 2) you might reach a peak with her and then the experiences may either "plateau" or begin to "decrease" in excitement. The analogy could be very well like being in a long term relationship where things just become "routine".
Now, if you go and try out several ladies, eventually you could have a few favourites that you like to have, and choose between them. That keeps the variety there, and I would think, really decreases the chances of you getting "bored" with anything. Each lady could offer something slightly different that you might seek at that time. Plus, it increases the chance of you being able to see someone, who might be available, when you're calling.
I think a lot of the guys have their favourites, see them somewhat regularly, and also see a few new ones too. You never know when you may end up adding to your "regular/favourites" with a new girl.