Warren Buffett is stockpiling cash. His Berkshire Hathaway holding company continued to sell more than it bought in the third quarter when it offloaded a quarter of its stake in Apple, regulatory filings revealed Thursday.

Warren Buffett passing on purchasing shares of Berkshire's stock when his company's cash pile is sitting at a record high ($325 billion) signifies that one of Wall Street's most ardent value investors is struggling to find a good deal. Berkshire's price-to-book value recently hit levels that haven't been consistently observed since 2008.

What is Warren Buffett's favorite stock? Other than the company he chairs, Apple ( AAPL -1.41%) may well be at the top of that list. The iPhone maker has been one of Buffett's largest holdings for years, even as he has decreased his stake in the tech company over the past 12 months.