If you are coming to the states, I have personal experience with two instructors. In 2012, I went to Madison, WI and took a 3-day lesson from Jerry Briesath. It was worth every minute and every dollar. He is not only an exceptional instructor, but probably one of the best human beings I've ever met. In 2016, I went to St. Louis, MO and took a couple days with Mark Wilson. I cannot say enough good things about Mark and his ability as an instructor. I went there specifically to work on my fundamentals and that is exactly what he honed in on. Again, worth every minute and every dollar. I have not had any direct personal experience with Dr. Dave, Bob Jewett, Scott Lee or Randy G., but based on things I've read about them, people I have talked to and products they have made, I seriously doubt you could wrong with any one of them. I'm sure there are others, but in my opinion, these are the cream of the crop. Good luck!