I like the ribs and brisket that I get at Costco. I usually buy my butts at Sams, they are about 30 cents a lb cheaper.
Sams has a better selection of restaurant supplies. If you are into vending that will make a difference.
Costco is closer so we go there most of the time. But Sams does have things that Costco doesnt. Ive never needed something that Sams didnt have but Costco did.