Investors looking for stocks in the Retail - Apparel and Shoes sector might want to consider either Tilly's (TLYS) or Gap (GPS). But which of these two companies is the best option for those looking for undervalued stocks? Let's take a closer look.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 proven Zacks Rank emphasizes companies with positive estimate revision trends, and our Style Scores highlight stocks with specific traits.Currently, both Tilly's and Gap are holding a Zacks Rank of # 1 (Strong Buy). 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 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.Our Value category grades stocks based on a number of key metrics, including the tried-and-true P/E ratio, the P/S ratio, earnings yield, and cash flow per share, as well as a variety of other fundamentals that value investors frequently use.TLYS currently has a forward P/E ratio of 14.30, while GPS has a forward P/E of 18.82. We also note that TLYS has a PEG ratio of 1.43. 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. GPS currently has a PEG ratio of 1.57.Another notable valuation metric for TLYS is its P/B ratio of 2.93. 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, GPS has a P/B of 4.22.These metrics, and several others, help TLYS earn a Value grade of B, while GPS has been given a Value grade of F.Both TLYS and GPS are impressive stocks with solid earnings outlooks, but based on these valuation figures, we feel that TLYS 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 Tillys, Inc. (TLYS): Free Stock Analysis Report The Gap, Inc. (GPS): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research