I'd definitely go with Costco, with BJ's as a second if it's much more convenient. I'm fortunate that my local Costco's gas is about $0.25 a gallon cheaper than the surrounding stations, so that savings alone pays for my membership.
all that means jack shit. Frankly i really odn't give a shit what the workers get paid.
When you pay a crappy wage and no benefits, you tend to get a revolving door of workers who don't give a shit. And that affects me very directly as a customer.
I've been a member of both clubs, and the quality of personnel is markedly better at Costco. That makes for a cleaner, more-organized store, and those motivated people run checkout lines that move a
hell of a lot faster than they do at Sam's.
The quality of merchandise is also significantly better at Costco, and you get a better value for your money because of it. The Sam's Club trash bags, for example, may be $0.75 less per box, but they're also cheaper bags that tend to rip more than the Costco ones. It's a very different corporate philosphy: Walmart seeks the lowest price regardless of quality, while Costco seeks the best quality for a given price point. As a consumer, I definitely notice the difference.
Walmart also manipulates its workers' pay and hours to have the government subsidize the employees. According to
this report from Congress, a single Walmart store saps anywhere from $904,542 to $1,744,590 in public benefits per year. You think you're getting a low price from them, when the truth is you're just paying it in your taxes instead.
So yeah, I do believe Walmart to be quite a bit more "evil" than Costco. And even if it weren't, it's still a crappy shopping experience compared to Costco.