I usually use 80 grit, but you will find you go through a LOT of it. Let the paper do the work, when you notice it's not cutting very well, change paper. Don't torture yourself by trying to get every last little bit out of your paper. It's a waste of time, effort, and wear and tear on your sander/compressor. Do save some of the used disks for fine detail and hand sanding, used disks work good for that.
