In reply to littlerich:
Depends what kind of cracks you like climbing. Finger cracks 1 or 1.5ish. Hand cracks 2.5 or 3ish. Fist cracks 3.5 or 4ish. Obviously horizontal break widths are very variable.
My most worn one seems to be the number 3, and I climb almost only on grit. Don't forget that hexes are a very good substitue for cams in a lot of placements.