Well, I don't have a horse. When I get one, I am most likely going to go for a slightly challenging horse, but one that knows what he is doing.
Right now, I do a little bit of finishing work on school ponies, trying to get a more desirable "school pony" product of them~ my current boy, for instance, he has behavioral issues at the canter and when jumping. So his owners only let people ride him walk trot, except for me while i'm working on him. I would rather ride him than any other horse... but when I can get a lesson on a well trained schoolmaster? I go for it. I learn a lot more on them than on Roger. There's really two different products for each answer; Buying/working with a green horse gives me satisfaction when they get something right or we get a little farther, and I love when they learn something new, but buying/working with a schoolmaster, I learn new things and I get a little farther. . Does that make sense?