Visa's competitive advantage should keep it in a leadership position for quite some time. Warren Buffett is one of the most accomplished investors in modern history, with a net worth of over $130 billion. Buffett and his partners have made Berkshire Hathaway a symbol of investing success and one of the top companies in the world. Berkshire Hathaway's stock portfolio consists of over 50 stocks covering many sectors. However, one of the companies that I'm all in on is Visa (V -0.80%). Visa accounts for less t ...