Investors with an interest in Financial - Investment Management stocks have likely encountered both Atlas (ATCO) and Blackstone Group (BX). 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 proven Zacks Rank emphasizes companies with positive estimate revision trends, and our Style Scores highlight stocks with specific traits.Currently, both Atlas and Blackstone Group are holding a Zacks Rank of # 2 (Buy). This means that both companies have witnessed positive earnings estimate revisions, so investors should feel comfortable knowing that both of these stocks have an improving earnings outlook. But this is just one factor that value investors are interested in.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.The Style Score Value grade factors in a variety of key fundamental metrics, including the popular P/E ratio, P/S ratio, earnings yield, cash flow per share, and a number of other key stats that are commonly used by value investors.ATCO currently has a forward P/E ratio of 11.53, while BX has a forward P/E of 21.75. We also note that ATCO has a PEG ratio of 0.77. 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. BX currently has a PEG ratio of 1.49.Another notable valuation metric for ATCO is its P/B ratio of 0.90. The P/B ratio pits a stock's market value against its book value, which is defined as total assets minus total liabilities. For comparison, BX has a P/B of 3.47.Based on these metrics and many more, ATCO holds a Value grade of A, while BX has a Value grade of D.Both ATCO and BX are impressive stocks with solid earnings outlooks, but based on these valuation figures, we feel that ATCO 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 Atlas Corp. (ATCO): Free Stock Analysis Report Blackstone Group IncThe (BX): Free Stock Analysis Report To read this article on Zacks.com click here.