Not all slabs are created equal, but value can be found in all of them.
The king of the market. PSA commands the highest resale value, but also the highest grading fees. Their red and white label is iconic.
Known for the "Tuxedo" black insert. SGC is gaining massive ground and is often preferred for vintage cards due to the contrast.
Famous for sub-grades. A BGS 9.5 "Gem Mint" was once the gold standard. They are still highly respected, especially for modern autographed cards.