My experience is that Costco is cheaper and entirely adequate/sufficient quality products, but rarely/never "top shelf" products (assuming that's meant to mean "the best").

This makes sense, as Costco is trying to move a lot of units and you can move a lot more units into the market that's looking for "perfectly adequate" than the ones looking for "the best". Honda outsells Porsche, Ferrari, and Lamborghini combined and all that...