Investors with an interest in Transportation - Shipping stocks have likely encountered both Costamare (CMRE) and Frontline (FRO). But which of these two companies is the best option for those looking for undervalued stocks? 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.Costamare and Frontline are both sporting a Zacks Rank of # 2 (Buy) right now. Investors should feel comfortable knowing that both of these stocks have an improving earnings outlook since the Zacks Rank favors companies that have witnessed positive analyst estimate revisions. But this is only part of the picture for value investors.Value investors also tend to look at a number of traditional, tried-and-true figures to help them find stocks that they believe are undervalued at their 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.CMRE currently has a forward P/E ratio of 10.16, while FRO has a forward P/E of 16.16. We also note that CMRE has a PEG ratio of 2.03. 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. FRO currently has a PEG ratio of 3.23.Another notable valuation metric for CMRE is its P/B ratio of 0.47. 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, FRO has a P/B of 1.12.These are just a few of the metrics contributing to CMRE's Value grade of B and FRO's Value grade of C.Both CMRE and FRO are impressive stocks with solid earnings outlooks, but based on these valuation figures, we feel that CMRE 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 Costamare Inc. (CMRE): Free Stock Analysis Report Frontline Ltd. (FRO): Free Stock Analysis Report To read this article on Zacks.com click here.