well...since liverystable.net is my favorite horses for sale site, horse article site, horse forum and horse blog, it only makes sense that my favorite trainer is Kevin Wescott!
you can see his site at http://www.kevinwescott.com
I wish he had more questions answered on liverystable.net, but I know Kevin personally, and he has really cut his clinics and horse training down as he is working as a missionary on the Rosebud Indian Reservation in South Dakota. But, that only helps speak to why I think he's a great trainer, because not only is he a great trainer, but an even better person.
I also think people like Curt Pate and Brent Graef are good trainers, but I'm personally not as interested in the trainers that are on RFD all the time - and there's a couple of them I can't stand at all. But I think there are terrible trainers and great trainers all over the place and probably it's impossible to know who the "best" is. I'd bet that if you knew the truth, the "best" is some little old 90 year old cowboy in Utah or Wyoming or wherever and no one except his family and neighbors will have ever heard of him!