Warren Buffett and Ken Griffin share a few things in common. First, they're both billionaires and highly respected investors. They're both also philanthropists.However, the two men have different investing styles  -- just look at their holdings. Buffett's Berkshire Hathaway portfolio includes only 43 stocks and exchange-traded funds (ETFs). Griffin's Citadel Advisors hedge fund owns positions in over 5,700 stocks and ETFs. There's some overlap in the two billionaire investors' portfolios, though -- even mor ...