I am a fan of Clinton Anderson. My geldings really catch on quick to his Method. Its easy to follow and don't get bored.
I took one gelding, Cosmo, to one of Shana Terry's 3 day clinic and it was great! We both learned so much. There was a couple of times that Shana had to yank a knot in his tail, but he ended up seeing it her way! Nothing cruel, nothing abusive.
I may not follow it daily or even weekly. But when they need a refresher on certain exercises, flexing, yielding or anything really. They both pick it up again very quickly and the little issues we were having are quickly solved.
This works for me. Study different methods and see what works for you and your horse. Good luck.