Most of my sketches I do with Mischief. It is pretty stripped down in terms of features, but it is all vector-based so you can scroll in/out/over as much as you like. I also use a wacom tablet.
Basically, I like not needing to keep adjusting my canvas size/resolution in photoshop, while still being able to fade layers. (ex, draw in a gesture sketch, fade it. draw structure over it, fade it. draw in details, ect...)