Investors with an interest in Financial - Investment Management stocks have likely encountered both Affiliated Managers Group (AMG) and Artisan Partners Asset Management (APAM). But which of these two companies is the best option for those looking for undervalued stocks? 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 favors stocks with strong earnings estimate revision trends, and our Style Scores highlight companies with specific traits.Right now, both Affiliated Managers Group and Artisan Partners Asset Management are sporting a Zacks Rank of # 2 (Buy). This system places an emphasis on companies that have seen positive earnings estimate revisions, so investors should feel comfortable knowing that these stocks 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.AMG currently has a forward P/E ratio of 7.89, while APAM has a forward P/E of 12.75. We also note that AMG has a PEG ratio of 0.53. 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. APAM currently has a PEG ratio of 0.63.Another notable valuation metric for AMG is its P/B ratio of 1.50. 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, APAM has a P/B of 26.96.These are just a few of the metrics contributing to AMG's Value grade of A and APAM's Value grade of C.Both AMG and APAM are impressive stocks with solid earnings outlooks, but based on these valuation figures, we feel that AMG 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 Affiliated Managers Group, Inc. (AMG): Free Stock Analysis Report Artisan Partners Asset Management Inc. (APAM): Free Stock Analysis Report To read this article on Zacks.com click here.