I don’t mind what Costco has, but it’s far from the best. I find most of their products are lower quality. Their Kalamata olives in the jar for instance are good for adding to things, but not for eating by themselves. Their 80/20 ground beef is way, way fattier than the 80/20 beef I buy at the local market. Their steaks are hit and miss. Most are bland. Their oils are OK, but nowhere near the best oils.
They are much cheaper, though.
They have good cheeses, although the sizes are too much for us to buy usually.
You also have to watch for Omega 6 oils in a lot their stuff, such as anything prepared. A lot of their olives and other similar products have canola or other higher Omega 6 or GMO oils.