I guess I will input :P
I have one finished horse and one very green horse.
I prefer my green horse over my finished one and would probably never buy a finished horse. The only reason behind that statement is that I don't show. I have no desire to compete at higher levels, or anything higher than a schooling show for that matter. I would feel like I was completely wasting a finished horse if I had one.
I believe that finished horses, in a certain discipline, should be used to their full potential in that discipline. I would not use them.
My finished horse has some bad habits that I can't really train out of him. He is older and retired now, but we had a lot of limitations due to how he was trained. He was doing higher level eventing before I ever got him and is extremely hot on a cross country course. Rearing and the like. Behavior that I would prefer not to deal with. He also doesn't do well in wide open spaces, constantly fights you and wants to run. He is all about speed and it drives me insane. No matter what you do with him, he doesn't get it. Also with his jumping, he won't let you moderate him. He decides when to take off, he decides where to take off, etc. You can't shorten or lengthen his stride. He has a shut up and hold on for the ride type of attitude.
My greenie on the other hand knows nothing. And by nothing, I mean literally nothing. He was track trained and had no idea what rein aids, leg aids, or anything like that were. I have put 5 rides on him so far and am having so much fun with him. He is a joy to ride and is learning so quickly. I like the idea of being able to train him the way I want him trained.
Because I am not an avid show-er I get more enjoyment out of learning to train a horse than from riding a trained horse. If I do show my greenie, it will be to show off how great he is and to promote OTTB's. My goal with him is to show people that a 3 year old OTTB can be an amazing horse. He is calmer, more responsive, and easier to ride than my 24 year old, fully trained gelding.
It is all about where you are with your riding and what you want to do. I wanted to learn to train and have a project to show for it. So that is what I am doing. If you want to show and win, then a trained horse would be the better option of course