Coming from a family where we have memberships at both competing bulk, membership only warehouses, at times it's pretty cool since both Sam's and Costco complement each other. Depending on the location you shop at, merchandise and certain brands differ. The prices at Sam's are comparable with Costco's, some things offered are cheaper or slightly more.
Like Costco, depending on the time and day you're at their store, food samples are available for a bite. Unlike Costco, I think with Costco it's because of customer volume compared to Sam's the food samples handed out are much larger and at times snack size. Unlike their Wal Mart counterparts, Sam's for the most part is organized, and neat.
Also like the gas stations attached to the store. they're substantially less than regular gas stations. Their store hours are much later than Costco as well, until 8:30p M-Sat. Overall I enjoy my membership with Sam's Club.