We have memberships at both Costco and Sam's. We had some not so satisfying experiences at Costco with some tough steaks and end up buying most of our meats from Sam's. The pork loin ribs are awesome - 3 racks to a cryopack. Can't believe how much meat is on those suckers. I'm lucky to finish half a rack.
With the whole brisket, the flat is definitely the premium section, but the point has awesome flavor and if you get the internal temp high enough can become quite tender as well. When I get done trimming out the heavy sections of dense fat between the flat and point they're barely connected anymore. After cooking I complete the separation to slice them since the muscle fibers run in different directions.
Favorite bottled sauce at the moment is Guy Fieri's Kansas City. Mixed that with de-fatted pan drippings and some Stubb's Spicy (habanero, cayenne, and black pepper) in a sauce pan. I try to avoid high-fructose corn syrup in my diet.