I had a friend that won use of Exiss for a year. That would have been 2000 model or late 99. She didn't like it much.
I have like the Keifer trailers that I have been around, but don't know much about 4-Star, although have heard good things about Sooner?
Best thing to me, would be to settle on years you are interested in, and then peruse the for sale ads, seeing which ones have held their value the best. And also type in search bar "problems with Sooner horse trailers" and also do the same for 4-Star trailers, or any that you are interested in, that way you will see if there are recalls, or problems before you commit.
Horses make me a better person.