Investors with an interest in Internet - Services stocks have likely encountered both 21Vianet (VNET) and The Trade Desk (TTD) . But which of these two stocks presents investors with the better value opportunity right now? Let's 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 pos ...