We frequented both for many years and I would say neither is "better" just different. We stuck with Costco in the end because it was closer and had cheaper gas prices. I don't think the gas prices are that good anymore.
Sam's benefits: opens MUCH earlier, 7am. I hate waiting for Costco to open at 10am. When you have little kids, you're up anyway! (and need to be home by naptime!)
Smaller quantities. I don't need 1000 paper plates, 500 is fine haha. Some fruits from Costco will go bad by the time you eat them, so you are really paying for waste.
Costco benefits: IMO better quality of food and more diversity/selection.
As for the pricing, no complicated math necessary. Sams, Costco and all grocery stores have a "unit price" listed on the price tags on the shelves. You just compare that. You do have to go to all the stores and write those unit prices down, but no math. Instead of comparing the price AND size of all the juices, the unit price lets you know how much the juice costs "per ounce" so you never have to factor in the quantity.
Hope I helped! I know we went thru this years ago. Check out GFS too, great prices though a smaller store. But no membership fee!