Amazon or Costco or else

I've been ordering a lot of stuff lately from Amazon, from bluray movies, books, toys, to hair product, electronics and accessories, and even sub-woofer. Small or big, light or heavy, all came in within 2 business days by Amazon Prime free 2-day shipping, and no sales tax! Just about the time that I think I can buy everything from Amazon, I ordered a couple of the laundry detergents and fabric softeners. They are heavy shipments, all came in within 2 days, but the portions were much smaller than the ones I'd find at Costco or Target store at similar prices. OK, so I saved on sales tax, and a trip to the store, but paid more for less. That being said,  I think Amazon is changing the way people shop, the only advantage Cosco has right now is that they sell grocery, and Amazon doesn't and probably very hard to do so to compete. Movies, music, books, electronics, toys, etc., are perfect for Amazon shopping!