I prefer Sam’s.
I like both of them for different things. I love getting prime cuts in their meat department. We just had some prime ribeye caps from Costco on Saturday as a treat. We grilled them and topped with lump crab and homemade bearnaise sauce. As good as any fancy restaurant at a quarter of the price.
Sam’s will ship to me with my premium membership. That way I don’t have to spend gas to get to the store and back. It’s further away than Costco. I order non-perishables that way and they’re delivered to my front door in a couple of days.