Investors interested in Utility - Electric Power stocks are likely familiar with AES (AES) and Unitil (UTL). But which of these two stocks is more attractive to value investors? We'll need to take a closer look to find out.Everyone has their own methods for finding great value opportunities, but our model includes pairing an impressive grade in the Value category of our Style Scores system with a strong Zacks Rank. The Zacks Rank favors stocks with strong earnings estimate revision trends, and our Style Scores highlight companies with specific traits.AES and Unitil are sporting Zacks Ranks of #1 (Strong Buy) and #3 (Hold), respectively, right now. Investors should feel comfortable knowing that AES likely has seen a stronger improvement to its earnings outlook than UTL has recently. But this is just one factor that value investors are interested in.Value investors are also interested in a number of tried-and-true valuation metrics that help show when a company is undervalued at its current share price levels.The Style Score Value grade factors in a variety of key fundamental metrics, including the popular P/E ratio, P/S ratio, earnings yield, cash flow per share, and a number of other key stats that are commonly used by value investors.AES currently has a forward P/E ratio of 13.56, while UTL has a forward P/E of 25.30. We also note that AES has a PEG ratio of 1.49. This popular figure is similar to the widely-used P/E ratio, but the PEG ratio also considers a company's expected EPS growth rate. UTL currently has a PEG ratio of 5.80.Another notable valuation metric for AES is its P/B ratio of 2.44. The P/B ratio pits a stock's market value against its book value, which is defined as total assets minus total liabilities. For comparison, UTL has a P/B of 2.47.These are just a few of the metrics contributing to AES's Value grade of B and UTL's Value grade of C.AES has seen stronger estimate revision activity and sports more attractive valuation metrics than UTL, so it seems like value investors will conclude that AES is the superior option right now.Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report The AES Corporation (AES): Free Stock Analysis Report Unitil Corporation (UTL): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research