I am rather new to the world of internal cultivation; I only know of two good sources in these strange lands - Max Christensen and Jerry Alan Johnson.   I was hoping you could share what you consider the most potent source(s) in terms of practice - of course, each of us has our own particular constitution, ideals and natural inclinations, so this is not to be understood as a childish attempt to find the "best" system. It is simply an inquiry as to what have worked the best for you.