If you are young enough to have a 50-year investment time window and be around to see the results, congratulations -- you have quite possibly the greatest investing advantage out there. While there is a lot of margin for error with that long of an investment time horizon, the best bets you can make today are in companies with sustainable competitive advantages that will be around 50 years from now or even more. So to give people with an ultra-long investment time horizon some ideas, we asked three of our contributors to highlight a stock they see as a 50-year investment.