By Dan Weil While the S&P; 500 index has dropped 13% this year, the S&P; 500 Dividend Aristocrats index has slipped only 6%. Dividend stocks are outperforming amid the equity market’s volatility, as investors are thirsty for the regular income that these stocks can provide. While the S&P 500 index has dropped 13% so far this year, the S&P 500 Dividend Aristocrats index has slipped only 6%. The latter index includes stocks that have raised their dividends for at least 25 straight years. If you’re thinking of investing in the sector, here are two of Morningstar’s top-rated dividend-stock mutual …