its feel and ability to hit diagonals. Supers are better for MAME cabs if you play a lot of 4 way games and don't have a 4 way stick because the diagonals feel "rounder" but I think comps are better sticks over all. Im not a fan of the Ultimates, they feel like lightweight cheapies.
I have comps in all my stand up cabs except MsPac (obvi) and I like the Sanwas in my Neogeo.