It's hard to argue with the idea Warren Buffett is the greatest living investor. There's a reason he's called the Oracle of Omaha, and it's why many investors follow his every stock move, but often Buffett's investing advice is more one of "do as I say, not as I do." While Berkshire Hathaway does own dozens of companies because of the vast sums of money he invests, Buffett has put most of his eggs into one basket: Apple (NASDAQ: AAPL).