Hi Andrea, in my opinion there are many different country to learn how to train horse!
England: very classical horse riding school, deutch school more strict than england, USA for the forward movement and also hunter classes!
You really have a lot of choice! It all depends on which horse riding you prefer to learn! :)
Maybe you can go in England and after in The United states to see the differences.
I don't think there is an ideal place to learn how to train. I believe everyone has their own style/way of learning, and what I find best how I've learned to train horses is by listening to everyone, and reading everything.
I even think you could learn great things from people like Anky (dressage "rollkur queen").
Just because you mightn't like the person or a particular thing they do. If you hear them speak, listen! They may say one word that makes you go "ah ha" I get it now. Even exploring outside your discipline. I'm a English rider, but most of my techniques for breaking and training are from a western fellow. Create what you like and what you think makes sense, and never stop learning!