Investors with an interest in Manufacturing - General Industrial stocks have likely encountered both Flowserve (FLS) and Xylem (XYL). But which of these two companies is the best option for those looking for undervalued stocks? Let's take a closer look.Everyone has their own methods for finding great value opportunities, but our model includes pairing an impressive grade in the Value category of our Style Scores system with a strong Zacks Rank. The proven Zacks Rank puts an emphasis on earnings estimates and estimate revisions, while our Style Scores work to identify stocks with specific traits.Flowserve and Xylem are sporting Zacks Ranks of #2 (Buy) and #3 (Hold), respectively, right now. Investors should feel comfortable knowing that FLS likely has seen a stronger improvement to its earnings outlook than XYL 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.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.FLS currently has a forward P/E ratio of 18.21, while XYL has a forward P/E of 49.11. We also note that FLS has a PEG ratio of 3.61. This figure is similar to the commonly-used P/E ratio, with the PEG ratio also factoring in a company's expected earnings growth rate. XYL currently has a PEG ratio of 4.91.Another notable valuation metric for FLS is its P/B ratio of 2.35. 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, XYL has a P/B of 5.71.Based on these metrics and many more, FLS holds a Value grade of B, while XYL has a Value grade of D.FLS has seen stronger estimate revision activity and sports more attractive valuation metrics than XYL, so it seems like value investors will conclude that FLS is the superior 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 Flowserve Corporation (FLS): Free Stock Analysis Report Xylem Inc. (XYL): Free Stock Analysis Report To read this article on Zacks.com click here.