The S&P 500 Index ended 2015 down 0.7% for the year, better than the 7% decline the benchmark index hovered at in September as a result of the summer's market volatility, but far short of the 11% gain for 2014.

The markets were roiled in 2015 due to slowing growth in China and other global markets, slumping commodity prices and oil's continuous plunge, as well as geopolitical concerns in the Middle East. U.S. markets had the added uncertainty this year of whether the Federal Reserve would raise interest rates.

"Volatile and lackluster," was how Jeff Kravetz, investment director of the Private Client Reserve of U.S. Bank, described the markets this year. "It's been overall a disappointing year for investors, and I think a lot of that was due to the high volatility that we experienced over the summer and then more recently with the Fed on and off."

The Fed's decision to raise rates finally came to fruition in December, when the federal funds rate was increased by a quarter of a point. It was the first rate increase in nearly a decade.

Despite the tumultuous year for equities, the stocks listed below had outstanding performances in 2015. The technology sector dominated the list of the 10 best-performing stocks in 2015. The sector itself rose 4.3%, outperforming the S&P 500.

Can you guess which stock had the best performance in 2015? Here's the list of best-performing stocks of the year, paired with ratings from TheStreet Ratings, TheStreet's proprietary ratings tool.

TheStreet Ratings uses a quantitative approach to rating over 4,300 stocks to predict return potential for the next year. The model is both objective, using elements such as volatility of past operating revenues, financial strength, and company cash flows, and subjective, including expected equity market returns, future interest rates, implied industry outlook and forecasted company earnings.

Buying an S&P 500 stock that TheStreet Ratings rated a buy yielded a 16.56% return in 2014, beating the S&P 500 Total Return Index by 304 basis points. Buying a Russell 2000 stock that TheStreet Ratings rated a buy yielded a 9.5% return in 2014, beating the Russell 2000 index, including dividends reinvested, by 460 basis points last year.

When you're done be sure to check out mid-cap and small stocks to buy for 2016