First off, we use a lot of grinding grit in the optic shop, so my comments are based on industrial usage, along with my personal experience making mirrors at the shop after hours.
Of primary importance is the manufacturer of the compounds. In 15 years of working with grinding compounds, I've only been happy with two companies materials, as far as alum.oxide anyway, Microgrit, the BRAND name, and KC Abrasives. I would think that there are other companies that probably make a product just as good, but none with a price differential good enough to switch. These two brands are very consistent, though they use a slightly different grading system. ie 5u KC is equiv to 3u microgrit 9u KC """"""""""" 5u microgrit, etc.
We usually finish fused silica with 5u, harder stuff like crystal, and softer stuff, pyrex and Bk-7, we give a 9u. KC's 3u is one step smaller than Microgrit's, and is impractical to use (scratches) except in very controlled situations. For polishing out grey by hand, it's worth using KC 5u or Micro's 3u, as this will make hand polishing go faster.
Both these products are distributed by Salem. Their west coast sales are thru Patterson & Assoc, down in Orange Co. Ca. with who I'ved been working with for years.(I'll dig up their phone#) However, we buy in lots of 50-200lbs, so I'm not sure of their philosophy on small amounts. It's good to hear that the main office is willing to deal with ATM'ers.
I have no idea who's products WB is marketing, but their prices are steep.
The key point is how they deal with dividing up larger lots and the cleanliness of how they repackage. From comments on this list, there do seem to be concerns.