Core mutual funds, which invest in both growth and value stocks, have led growth-focused and value-centric funds in performance for much of the past 10 years. An investment of $10,000 in the average core mutual fund on June 30, 2005, would have grown to $24,427 by July 2 this year, vs. $23,880 for the average growth fund, $18,846 for its value counterpart and $21,524 for the S&P 500, according to Morningstar Inc. data.