Investors looking for stocks in the Medical - Biomedical and Genetics sector might want to consider either Vertex Pharmaceuticals (VRTX) or Prothena (PRTA). 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 puts an emphasis on earnings estimates and estimate revisions, while our Style Scores work to identify stocks with specific traits.Currently, Vertex Pharmaceuticals has a Zacks Rank of #2 (Buy), while Prothena has a Zacks Rank of #3 (Hold). Investors should feel comfortable knowing that VRTX likely has seen a stronger improvement to its earnings outlook than PRTA has recently. 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.The Value category of the Style Scores system identifies undervalued companies by looking at a number of key metrics. These include the long-favored P/E ratio, P/S ratio, earnings yield, cash flow per share, and a variety of other fundamentals that help us determine a company's fair value.VRTX currently has a forward P/E ratio of 17.84, while PRTA has a forward P/E of 235.27. We also note that VRTX has a PEG ratio of 1.50. This metric is used similarly to the famous P/E ratio, but the PEG ratio also takes into account the stock's expected earnings growth rate. PRTA currently has a PEG ratio of 100.98.Another notable valuation metric for VRTX is its P/B ratio of 5.77. 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, PRTA has a P/B of 8.83.These are just a few of the metrics contributing to VRTX's Value grade of B and PRTA's Value grade of D.VRTX stands above PRTA thanks to its solid earnings outlook, and based on these valuation figures, we also feel that VRTX is the superior value option right now. More Stock News: This Is Bigger than the iPhone! It could become the mother of all technological revolutions. Apple sold a mere 1 billion iPhones in 10 years but a new breakthrough is expected to generate more than 77 billion devices by 2025, creating a $1.3 trillion market. Zacks has just released a Special Report that spotlights this fast-emerging phenomenon and 4 tickers for taking advantage of it. If you don't buy now, you may kick yourself in 2022.Click here for the 4 trades >>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 Vertex Pharmaceuticals Incorporated (VRTX): Free Stock Analysis Report Prothena Corporation plc (PRTA): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research