My standard purfling system for 1A guitars has the last 3 - 4 years been what I call the window. It frames each of the 2 parts of the back and the sides with purling on the inside, everything neat and with 45 degrees mitering. Its a very difficult way to do the purfling, but its also very elegant and prestigeous. The most problematic part is the burfling on the back because it has to be cut very precisely in both ends.
On the other hand, when I build a 2A, I dont use purfling on the back and sides, and there´s something about that, that I really like. Simplicity and contrast.