Just found this link...
http://reviews.ebay.com/Buying-Grade...00000001342856
It indicates the following:
Sports Collectors Digest Authentic (SCD) - now out of the grading business, SCD was generally considered to be a reputable and accurate service. On the open market, you will still find the odd SCD graded card, distinguishable by the red logo on the silver label. CAUTION: there is a new "SCD" (Sports Cards Direct) that uses a similar silver label but with blue logo. This new service is not considered to be a reputable grading company.
However it also states the following about GAI:
Global Authentication (GAI) - Started by two former PSA employees, GAI is the relative new kid on the grading block, and as such they have a smaller market share than the other companies. My personal experience with GAI is limited, but positive, and general consensus is that they do a reputable job of grading. However, GAI, like SGC, has more of a reputation with vintage cards and little market share among modern card grading.
I'm sorry but I'd trust the Sports Collectors Digest grading more than the GAI slabs.
Also in the linked page:
Companies NOT to be considered:
GEM, GEM Elite, MINT, RARE, PRO, USA, CSA, AGS, PGS, GradeMyCards, FGS, GMA, IGS, NASA, WCG, 3-D, Grading Unlimited, CGE, GRA, ASA, SPA, TFA, PGI, etc.
Quite literally, some of these companies don't exist for more than a year, develop a reputation, rebrand themselves and start over. This list only hints at the number of illegitimate grading operations out there.
Even worse, some of these "grading" companies area actually basement slabbing operations, with the "grader" selling his own slabs online.
Ask yourself this: if you owned a Mickey Mantle rookie card that you absolutely knew was authentic and unaltered, why would you send it to a grading company that had anything less than a stellar reputation? Now ask yourself why that Mantle rookie on eBay is sitting in a slab from Bubba's Grading Service. The bottom line is that a card graded Poor by a reputable company is still more desirable than a trimmed card or a fake, no matter what numerical grade is on the label.