Investors interested in stocks from the Retail - Discount Stores sector have probably already heard of Target (TGT) and Costco (COST). But which of these two stocks is more attractive to value investors? We'll need to take a closer look to find out.We have found that the best way to discover great value opportunities is to pair a strong Zacks Rank with a great 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.Target has a Zacks Rank of #2 (Buy), while Costco has a Zacks Rank of #3 (Hold) right now. The Zacks Rank favors stocks that have recently seen positive revisions to their earnings estimates, so investors should rest assured that TGT has an improving earnings outlook. But this is just one piece of the puzzle for value investors.Value investors also tend to look at a number of traditional, tried-and-true figures to help them find stocks that they believe are undervalued at their current share price levels.Our Value category highlights undervalued companies by looking at a variety of key metrics, including the popular P/E ratio, as well as the P/S ratio, earnings yield, cash flow per share, and a variety of other fundamentals that have been used by value investors for years.TGT currently has a forward P/E ratio of 21.81, while COST has a forward P/E of 39.15. We also note that TGT has a PEG ratio of 3.02. This figure is similar to the commonly-used P/E ratio, with the PEG ratio also factoring in a company's expected earnings growth rate. COST currently has a PEG ratio of 4.61.Another notable valuation metric for TGT is its P/B ratio of 6.23. The P/B ratio is used to compare a stock's market value with its book value, which is defined as total assets minus total liabilities. For comparison, COST has a P/B of 8.87.These metrics, and several others, help TGT earn a Value grade of B, while COST has been given a Value grade of C.TGT sticks out from COST in both our Zacks Rank and Style Scores models, so value investors will likely feel that TGT is the better 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 Target Corporation (TGT): Free Stock Analysis Report Costco Wholesale Corporation (COST): Free Stock Analysis Report To read this article on Zacks.com click here.