We have memberships to both Costco and Sams, and through work my wife has a BJs membership too, and we use them all.
Not much to add to what has already been said above.
For us, the things that we prefer are split amongst them. Example: Sams has half gallon jars of slices jalapenos @ $3.25, and Costco doesn't have them. What I save at Sams, over the supermaket price, on Jalapenos alone almost covers the cost of that membership. Yeah, I use a lot ... put them in my salad every night.
I just pick which one I'm going to go to based on what will be most advantagous (depending on what I need) that wekend, and I am not averse to hitting two in one trip if my needs and the savings warrant it.
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