Investors interested in Staffing Firms stocks are likely familiar with ManpowerGroup (MAN) and Cross Country Healthcare (CCRN). 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 puts an emphasis on earnings estimates and estimate revisions, while our Style Scores work to identify stocks with specific traits.Right now, both ManpowerGroup and Cross Country Healthcare are sporting a Zacks Rank of # 2 (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 just one factor that value investors are interested in.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.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.MAN currently has a forward P/E ratio of 19.44, while CCRN has a forward P/E of 20.40. We also note that MAN has a PEG ratio of 0.90. 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. CCRN currently has a PEG ratio of 2.34.Another notable valuation metric for MAN is its P/B ratio of 2.77. 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, CCRN has a P/B of 3.31.Based on these metrics and many more, MAN holds a Value grade of A, while CCRN has a Value grade of C.Both MAN and CCRN are impressive stocks with solid earnings outlooks, but based on these valuation figures, we feel that MAN 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 ManpowerGroup Inc. (MAN): Free Stock Analysis Report Cross Country Healthcare, Inc. (CCRN): Free Stock Analysis Report To read this article on Zacks.com click here.