Binding before fretting, always. I've used a router to create the binding channel after installation, and I've also applied the binding to the board before attatching it. I like applying the binding to the board because then, when I'm doing the final planing to the underside of the board in preparation for the glueing, the binding is always perfectly straight, because it gets planed with the board. I don't have to worry about getting a good, tight fit against the back of the neck, or the board, like you do with a rabbet cut.