Amazon would be the one with the most competitors. Many Amazon sellers have their own websites, not to mention Aliexpress, Walmart, Target, HomeDepot, Bestbuy, Monoprice, Staples, Costco, etc.
I'm referring to competitors of the overall Amazon experience, not really the individual products, in which the main value proposition for me is the extremely fast shipping. Those other stores typically don't offer it at a reasonable price, because they don't have warehouses a stone's throw from most customers.
