Investors looking for stocks in the Insurance - Property and Casualty sector might want to consider either American Financial Group (AFG) or W.R. Berkley (WRB). But which of these two stocks presents investors with the better value opportunity right now? Let's take a closer look.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.American Financial Group and W.R. Berkley are both sporting a Zacks Rank of # 2 (Buy) right now. 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. However, value investors will care about much more than just this.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 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.AFG currently has a forward P/E ratio of 11.64, while WRB has a forward P/E of 24.60. We also note that AFG has a PEG ratio of 1.90. 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. WRB currently has a PEG ratio of 2.73.Another notable valuation metric for AFG is its P/B ratio of 1.60. 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, WRB has a P/B of 2.11.Based on these metrics and many more, AFG holds a Value grade of B, while WRB has a Value grade of D.Both AFG and WRB are impressive stocks with solid earnings outlooks, but based on these valuation figures, we feel that AFG 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 American Financial Group, Inc. (AFG): Free Stock Analysis Report W.R. Berkley Corporation (WRB): Free Stock Analysis Report To read this article on Zacks.com click here.