Costco usually has good prices on the brand names. The monthly coupons often feature Bounty towels or one of either Northern or Charmin TP. Kirkland paper towels and TP are not worth the money in my experience.
However, Target has some very good sales, which when combined with their coupons and the red card, often beat Costco. For example, I just ordered five bottles of Tide for $8.00 a bottle because of a $15 off $50 in household supplies purchase coupon, a sale in progress, the red card 5 percent, and free shipping. They often have large packs of paper goods on sale, plus buy two and get a $5.00 gift card.
I have given up trying to figure out which deal is the very cheapest, because of the games manufacturers play with quantity (have you noticed how much toilet paper rolls have shrunk in width?). I just look at the price and my best guess at quantity and say good enough.