The e-commerce giants have many similarities.Both Amazon (AMZN 0.33%) and Shopify (SHOP 0.60%) are incredible businesses. Both target e-commerce spending, which has grown at double-digit percentage rates for years, and is expected to do so for years to come. When it comes to high-upside stocks, both of these companies fit the bill. But which stock has the potential to deliver the biggest profits to those who buy in today?Amazon has achieved greatness -- and that's a bit of a problemAmazon needs no introduct ...