Investors interested in Medical - Drugs stocks are likely familiar with Collegium Pharmaceutical (COLL) and Zoetis (ZTS). But which of these two stocks presents investors with the better value opportunity right now? Let's take a closer look.The best way to find great value stocks is to pair a strong Zacks Rank with an impressive grade in the Value category of our Style Scores system. The Zacks Rank is a proven strategy that targets companies with positive earnings estimate revision trends, while our Style Scores work to grade companies based on specific traits.Collegium Pharmaceutical and Zoetis are sporting Zacks Ranks of #1 (Strong Buy) and #3 (Hold), respectively, right now. The Zacks Rank favors stocks that have recently seen positive revisions to their earnings estimates, so investors should rest assured that COLL has 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 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.COLL currently has a forward P/E ratio of 5.31, while ZTS has a forward P/E of 43.84. We also note that COLL has a PEG ratio of 0.27. 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. ZTS currently has a PEG ratio of 3.17.Another notable valuation metric for COLL is its P/B ratio of 2.76. 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, ZTS has a P/B of 21.62.Based on these metrics and many more, COLL holds a Value grade of A, while ZTS has a Value grade of C.COLL stands above ZTS thanks to its solid earnings outlook, and based on these valuation figures, we also feel that COLL is the superior value option right now. Breakout Biotech Stocks with Triple-Digit Profit Potential The biotech sector is projected to surge beyond $2.4 trillion by 2028 as scientists develop treatments for thousands of diseases. They’re also finding ways to edit the human genome to literally erase our vulnerability to these diseases. Zacks has just released Century of Biology: 7 Biotech Stocks to Buy Right Now to help investors profit from 7 stocks poised for outperformance. Recommendations from previous editions of this report have produced gains of +205%, +258% and +477%. The stocks in this report could perform even better.See these 7 breakthrough stocks 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 Collegium Pharmaceutical, Inc. (COLL): Free Stock Analysis Report Zoetis Inc. (ZTS): Free Stock Analysis Report To read this article on Zacks.com click here.