Investors with an interest in Internet - Services stocks have likely encountered both Rakuten, Inc. (RKUNY) and Shopify (SHOP). 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 proven Zacks Rank emphasizes companies with positive estimate revision trends, and our Style Scores highlight stocks with specific traits.Rakuten, Inc. has a Zacks Rank of #2 (Buy), while Shopify has a Zacks Rank of #5 (Strong Sell) right now. This means that RKUNY's earnings estimate revision activity has been more impressive, so investors should feel comfortable with its improving analyst outlook. But this is just one piece of the puzzle for value investors.Value investors analyze a variety of traditional, tried-and-true metrics to help find companies that they believe are undervalued at their 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.RKUNY currently has a forward P/E ratio of 19.87, while SHOP has a forward P/E of 461.56. We also note that RKUNY has a PEG ratio of 2.65. 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. SHOP currently has a PEG ratio of 19.50.Another notable valuation metric for RKUNY is its P/B ratio of 1.86. 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, SHOP has a P/B of 10.43.Based on these metrics and many more, RKUNY holds a Value grade of A, while SHOP has a Value grade of F.RKUNY has seen stronger estimate revision activity and sports more attractive valuation metrics than SHOP, so it seems like value investors will conclude that RKUNY 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 Rakuten, Inc. (RKUNY): Free Stock Analysis Report Shopify Inc. (SHOP): Free Stock Analysis Report To read this article on Zacks.com click here.