Investors interested in Retail - Discount Stores stocks are likely familiar with Dollar General (DG) and Ross Stores (ROST). But which of these two stocks presents investors with the better value opportunity right now? Let's take a closer look.There are plenty of strategies for discovering value stocks, but we have found that pairing a strong Zacks Rank with an impressive grade in the Value category of our Style Scores system produces the best returns. The Zacks Rank is a proven strategy that targets companies with positive earnings estimate revision trends, while our Style Scores work to grade companies based on specific traits.Both Dollar General and Ross Stores have a Zacks Rank of # 2 (Buy) right now. The Zacks Rank favors stocks that have recently seen positive revisions to their earnings estimates, so investors should rest assured that both of these companies have improving earnings outlooks. But this is just one piece of the puzzle for value investors.Value investors also try to analyze a wide range of traditional figures and metrics to help determine whether 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.DG currently has a forward P/E ratio of 19.84, while ROST has a forward P/E of 114.68. We also note that DG has a PEG ratio of 1.45. This popular metric is similar to the widely-known P/E ratio, with the difference being that the PEG ratio also takes into account the company's expected earnings growth rate. ROST currently has a PEG ratio of 11.47.Another notable valuation metric for DG is its P/B ratio of 7.23. 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, ROST has a P/B of 13.46.These metrics, and several others, help DG earn a Value grade of B, while ROST has been given a Value grade of D.Both DG and ROST are impressive stocks with solid earnings outlooks, but based on these valuation figures, we feel that DG is the superior value 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 Dollar General Corporation (DG): Free Stock Analysis Report Ross Stores, Inc. (ROST): Free Stock Analysis Report To read this article on Zacks.com click here.