Investors with an interest in Security stocks have likely encountered both Zix (ZIXI) and Palo Alto Networks (PANW). But which of these two stocks offers value investors a better bang for their buck right now? We'll need to 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, Zix is sporting a Zacks Rank of #2 (Buy), while Palo Alto Networks has a Zacks Rank of #3 (Hold). This means that ZIXI's earnings estimate revision activity has been more impressive, so investors should feel comfortable with its improving analyst 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.ZIXI currently has a forward P/E ratio of 11.81, while PANW has a forward P/E of 48.64. We also note that ZIXI has a PEG ratio of 0.79. 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. PANW currently has a PEG ratio of 2.08.Another notable valuation metric for ZIXI is its P/B ratio of 10.27. 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, PANW has a P/B of 31.20.These metrics, and several others, help ZIXI earn a Value grade of B, while PANW has been given a Value grade of D.ZIXI is currently sporting an improving earnings outlook, which makes it stick out in our Zacks Rank model. And, based on the above valuation metrics, we feel that ZIXI is likely 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 Zix Corporation (ZIXI): Free Stock Analysis Report Palo Alto Networks, Inc. (PANW): Free Stock Analysis Report To read this article on Zacks.com click here.