Investors looking for stocks in the Utility - Gas Distribution sector might want to consider either MDU Resources (MDU) or Atmos Energy (ATO). But which of these two stocks is more attractive to value investors? We'll need to take a closer look to find out.The best way to find great value stocks is to pair a strong Zacks Rank with an impressive grade in the Value category of our Style Scores system. The Zacks Rank favors stocks with strong earnings estimate revision trends, and our Style Scores highlight companies with specific traits.MDU Resources has a Zacks Rank of #2 (Buy), while Atmos Energy has a Zacks Rank of #3 (Hold) right now. This means that MDU's earnings estimate revision activity has been more impressive, so investors should feel comfortable with its improving analyst outlook. But this is only part of the picture for value investors.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 Value category of the Style Scores system identifies undervalued companies by looking at a number of key metrics. These include the long-favored P/E ratio, P/S ratio, earnings yield, cash flow per share, and a variety of other fundamentals that help us determine a company's fair value.MDU currently has a forward P/E ratio of 13.60, while ATO has a forward P/E of 19.79. We also note that MDU has a PEG ratio of 1.97. 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. ATO currently has a PEG ratio of 2.72.Another notable valuation metric for MDU is its P/B ratio of 1.68. The P/B is a method of comparing a stock's market value to its book value, which is defined as total assets minus total liabilities. By comparison, ATO has a P/B of 1.69.These are just a few of the metrics contributing to MDU's Value grade of B and ATO's Value grade of D.MDU stands above ATO thanks to its solid earnings outlook, and based on these valuation figures, we also feel that MDU is the superior value option right now. Just Released: Zacks Top 10 Stocks for 2022 In addition to the investment ideas discussed above, would you like to know about our 10 top picks for the entirety of 2022? From inception in 2012 through 2021, the Zacks Top 10 Stocks portfolios gained an impressive +1,001.2% versus the S&P 500’s +348.7%. Now our Director of Research has combed through 4,000 companies covered by the Zacks Rank and has handpicked the best 10 tickers to buy and hold. Don’t miss your chance to get in…because the sooner you do, the more upside you stand to grab.See Stocks 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 MDU Resources Group, Inc. (MDU): Free Stock Analysis Report Atmos Energy Corporation (ATO): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research