I have a horse trained by an old-school Parelli instructor and the horse is amazing and the trainer was amazing. I give a lot of credit to the trainer, who was a true horseman. Interestingly, he had dropped his official Parelli instructor license or brand or whatever because the Parellis make their 'licensed' instructors use ONLY Parelli techniques or else they can't carry the Parelli brand. Surprised, anyone?
I think Clinton Anderson has been so successful because has people skills. He can actually teach. He tells you what he's doing, shows you what he's doing, gets the crowd to recognize what's he's doing and say it back to him, and as adults that how we learn best. We can see "the moment" when we should be releasing pressure. Not so much the Parelli's. John Lyons is a great horseman, and a really nice guy from what I have seen, but his methods are hard for me to see "the moment." He uses a lot of rein work and not so much leg aids (because his knees were shot and he couldn't use his legs without intense pain). I do use his desensitizing methods, and I love his teaching that your horse doesn't have to stop and stare at the scary thing, he has to walk on as if it isn't there. That's the goal.
I also like Julie Goodnight. For those of you who are English and dressage disciplines, she started as an English rider, working with racehorses; has done work on dressage horses, and of course also does Western. She is a good teacher - and a great horsewoman. Lately she has been pushing Myler bits and that turned me off at first (I don't like the idea that you have to have certain brands of equipment). However, her goal was to show WHY the bit change was helpful and I used that lesson, changed my gelding's bit and (knock wood) think I am on the way to successfully turning a sour gelding into a happy gelding with that result. She is really big on pre-signals - and I think the idea of pre-signals has changed the way I deal with my horses. BTW, the Ray Hunt/Dorrance horsemen used pre-signals, too, so this has roots in the original natural horsemanship methods.
Agree that Chris Cox is good - he tells it like it is. I laughed my tush off when he was talking about women talking on trail rides and not "riding" their horses. Cannot understand Dennis Reis although he's effective, can't argue with that. His stuff is pricey so I haven't shelled out for the DVDs.
Would add that Ken McNabb is also a solid horseman, from the John Lyons school originally, and he is a great teacher. I have been to several of his clinics and I really like his methods. Nothing fancy, he gets his ideas across. He has some DVDs on his web site too.
Bottom line, I think it does not matter one whit what the clinicians can do by themselves. If they cannot TEACH in a way that YOU can use their techniques and have a happier, more productive horse, you haven't found the right combination yet. They have to be able to get their ideas across to you.
And, I agree that you can pick up great tips and techniques from lots of different people. The best trainers and clkinicians will admit that they are always learning, always incorporating different ideas all the time...