Which of these powerful American brands is the better investment?Nike (NKE 1.94%) and Coca-Cola (KO -0.58%) are two of the most iconic brands in America. Nike is the world's largest supplier of athletic footwear and apparel, while Coca-Cola is one of the biggest beverage companies.But over the past three years, Nike's stock declined by more than 50% while Coca-Cola's shares advanced nearly 20%. Let's see why the soda titan outperformed the footwear maker -- and whether it's still the better stock to buy rig ...