T206 collector gave an excellent summary of SGC's benefits, I just thought I'd add the following:
- No Subscription Service: PSA makes you pay an annual membership fee, which you have to maintain whether or not you want to submit cards. SGC is a straight up pay for grading service, its simple, easy, and gimmicky no long term commitments. However, if you only plan on buying graded cards, and not submitting raw cards, then this isn't an issue.
- One more vote for consistent grading: I've seen some awful cards in high grade PSA holders. SGC is definitely more consistent on their grading.
- The SGC holder is the best! The SGC holder is beautiful way to display your cards. Its black background makes the white bordered T206 really stand out. The PSA holder is ugly in my opinion. First, it is clear, with an ugly red label, and there is a little piece of plastic that covers up the bottom of the card. I don't like it.
- Customer Service! Its amazing, but you can call up SGC and talk to a real person, every time, usually the same guy (Brian), they just really take care of you. As I stated above, if you only plan on buying graded cards, and not submitting raw cards, then this isn't an issue.
That said, PSA cards are more common on eBay, so if you don't want to cross cards over to SGC, and want to acquire a collection quickly, and you like the PSA holder, then go PSA.