re: Costco or Sam's?

Costco's sample day is better than Sam's. Other than that, as a whole there is no real difference. As others have said, some Kirkland's branded items like clothing and food are better than their Member's Mark brethren, but when it comes to bulk items like paper plates and paper towels you're going to get a better deal on Sam's brands.

We've got memberships to both and simply buy from the one with the best deal for what we need.