There is a new generation of air disc brakes coming from Europe lately, and from all I hear they are working great, and we should expect to see more and more of them. It's these brakes I want, as they will soon be offering them to fit in a 19.5" wheel package (already do in Europe).
I have also heard that the first generation air disc brakes were not much good. But sounds like they have it figured out now.
Grigg