Ken - Don't know if you're talking about sanding discs, but there was a side by side comparison done on discs.
It came out of a magazine so I don't have it handy to post online, but the basis of the comparison was the "cost to remove one gram of wood." It was the fairest way to rate them, I thought, because it took into consideration your end net-cost of using them, and not the shelf price (i.e. discs that are higher priced may well last longer, etc.)
3M Sand Blaster, although it stays clean, was the worst - about 9 cents per gram. Klingspor was the best at around 3 cents I believe. I order them online from the Klingspor siter at $12 for a box of 50.
Norton 3X was right behind Klingspor.
I did rub my brother-in-laws nose in the Sand Blaster because he's a retired 3Mer and still thinks they walk on water, as well as everyone who works there.