[vintagetoppsguy]

If you're grading the cards for your own personal collection, go with whichever one you find more aesthetically pleasing. Some cards look better in PSA slabs, some look better in SGC slabs.

If you're grading to re-sell, the edge goes to PSA. Their slabs realize higher prices.

If you're looking to buy cards already graded, go with SGC. They're grading is more consistent and their cards sell for less than they're PSA counterparts.