The retail industry is a fiercely competitive arena. Winners can quickly become losers, and only the strongest retailers tend to survive over the long term. Yet the businesses that do endure and prosper can earn their investors a fortune. Best-of-breed retailers Amazon (NASDAQ:AMZN), CarMax (NYSE:KMX), and Apple (NASDAQ:AAPL) have done just that, and are poised to continue to do so for years to come.

Amazon is an increasingly dominant force in the retail arena. The e-commerce titan offers its customers a value proposition -- including a wide selection of products, low prices, and a convenient shopping experience -- that its competitors can't match. That powerful combination has served Amazon and its investors well, and its stock has been a multi-bagger many times over since its IPO on May 16, 1997. 

Yet I believe that far more gains lie ahead. As Amazon's tremendous scale and reach grow larger, so does its competitive advantages over rival retailers. For example, Amazon's heavy investments in its massive fulfillment network are likely to pay increasing dividends in the years ahead, as next-day and same-day delivery options allow Amazon to offer its customers even more convenience. That, in turn, should result in further market-share gains for Amazon as it reduces one of the last remaining advantages -- immediacy -- that brick-and-mortar retailers still enjoy relative to the online juggernaut.

Amazon's best-in-class customer service helps to further strengthen its brand and consumer mindshare. In fact, is increasingly becoming the first -- and last -- place people go to shop online. That should only grow more valuable in the years ahead as e-commerce grows both in absolute terms, and as a share of total retail sales. E-commerce only accounted for 5.9% of global retail sales in 2014, yet is expected to rise to 8.8% of the estimated $28.3 trillion total worldwide retail sales in 2018 as per eMarketer.

With so much growth still to come, the Internet shopping megatrend remains in its early innings. Amazon is one of the best-positioned businesses to profit from this massive trend -- if not the best.

Source: Carmax.

Profitable investments can often be found in companies that offer a better way forward in an old, boring -- and even better -- hated industry. Few retail-shopping experiences are despised more than buying a used car, and therein lies CarMax's opportunity.

CarMax's no-haggling approach is a far cry from the unpleasant -- and sometimes deceptive -- practices many car shoppers are forced to endure at other car dealerships. CarMax's helpful employees, fair pricing, and wide selection of vehicles all help to delight its customers, with 95% of customers saying they would recommend CarMax to a friend. 

CarMax's stock has risen more than 500% from its IPO on Feb. 4, 1997, with much of those returns occurring in the last five years. Yet it's CarMax's future growth potential that I find most intriguing. With only about 5% of the highly fragmented used-car market, CarMax has a long runway ahead to continue to gobble up market share from less customer-friendly rivals.

Source. Apple.

Apple may not be what first pops into your mind when you think of retail stocks, but make no mistake: The world's largest publicly traded company is also one of its most successful retailers. Apple stores generate some of the highest sales per square foot in the entire retail arena, and they've become an important differentiator for Apple's brand. 

Apple excels at positioning its stores in prime locations, and then carefully designs each store so as to match its surrounding environment and appeal to local culture. But it's not just the beautiful architecture that distinguishes these stores; Apple's retail employees are known for giving un-rivaled attention to the customer, which further helps to differentiate the Apple retail-shopping experience. 

Maybe most importantly, Apple stores give millions of people around the world the opportunity to see and feel Apple's devices. This tactile experience no doubt helps to convert more consumers into customers, and thanks to Apple's excellent customer satisfaction ratings, many of them will likely remain in Apple's ecosystem for many years to come.