Perhaps the finding the "Best" American style longbow is a fools errand given the individual preference/mechanics involved in the best for any individual archers.
However, having said that there are definitely several bowyers that have their 10,000 hours in...
James Berry has been at it for 32 years and is really at the top of his came right now. I have seen him build in the shop and he is an artesian from another age in terms of the intensity and attention he puts into his builds and the standards he holds for his bows. His bows show and preform to these high standards.
I know I am bias, but I vote the Vixen, the Morning Star and/or the Northstar ( I have not shot the Misty Dawn).
I have shot other makes and models (Hill, Robertson, Toelke, etc) and I know there are other beauties out there for sure, but JD Berry's American style longbows are unquestionably world class. When I pick one of my bows up I can feel the history, the power and the craftsmanship in each bow and in every shot.