While the stocks of Google and Facebook are both up over 20 percent year to date, Mahaney favors Google's outlook.
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Although shares of Facebook have seen a couple of nice rallies in the past year, the upside hovers between 10 and 15 percent, Mahaney said. Meanwhile, owners of stock in Google, which returns cash to shareholders, can see returns of 20 to 25 percent, he said.
Plus, Mahaney said, Google is well-positioned to match job offers dollar for dollar with unicorn companies, and under the new Alphabet umbrella, there are more leadership titles to incentivize top-notch coders to stick around.
Another big focus for Mahaney: Now that many of the FANG stocks are trading close to their peaks, it makes it more difficult to create upside, with shares of Netflix, for instance, up 91 percent over the past year.
"Take that Netflix stock, that was at the top of our list earlier this year," he said. "It can't be one of our top picks now, just given the rise in valuation and stock price."
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