It's hard to buy food there because our household isn't large enough to buy fresh food in bulk but hard goods, sure. And I don't really save money on them. but I also don't have to shop to TP every month...
And as has been pointed out, great customer service and a fantastic return policy. Lots of member benefits (counter tops, tires, blinds, car rentals)
My rebate pays for my member fee.
Now to be fair, my (local) Smith's has great service, as does Sprouts, where I shop most frequently, but for what it has, yeah, Costco is "best" IMO.
That the employees are pleasant, and helpful, and happy to be there, and actually get paid a living wage, well, that's all a bonus.