Patrick Costello. First, he's personable. Secondly, he makes a sincere effort to be thorough in his teaching. Thirdly, he enjoys teaching his subject, and fourthly he knows a lot, and tries to give the banjo respect as a musical instrument, rather than just give it the old "What the heck, it's just a banjo" treatment.
His main premise seems to be that one has to have in one's head a minimal amount of music theory, either formally or intuitively ( preferably the former, I think, but I'm a mathematician, not a musician). For instance, he answers the question we see so often here: "What good are chords"? He also, in only his second lesson, relates frailing the banjo to the old time way of playing the guitar ( and I thought I invented that).
Patrick obviously loves teaching us music, and he has my deepest appreciation for doing that, and making the lessons freely available to us on youtube. Maybe it's because I'm a retired teacher of mathematics that I like his way of doing things, but I think not. I think it's because he has a lot to say to an aspiring banjo player, and he says it very, very well.