Facebook's fastest growth days are behind it, investor says

In the battle of the big tech stocks, Facebook's peak growth rate could be in the past, a portfolio manager told CNBC's "Squawk Alley" Monday.

"While we still like Facebook, we think their fastest growth days are probably behind them, although we still expect them to be a significant grower in the future, just albeit slightly decelerating," Brad Slingerlend, portfolio manager of the Janus Global Technology strategy, said Monday.

Slingerlend's fund holds "significant positions" in technology darlings Facebook, Apple, Alphabet's Google and Amazon. But while Facebook shares have bounced 44 percent in the past year, Slingerlend has trimmed that position in favor of Google and Amazon, up 29 percent and 64 percent year-over-year, respectively.

"Social media has been a little bit more fickle," Slingerlend said. "We see a lot of folks, particularly the younger generation, moving to Snapchat in the U.S., away from Facebook and Instagram. Obviously Twitter is seeing ... usage slowing down. So it's a little bit harder to have confidence in social networking longer term."

But Slingerlend said Google's offerings, like search, could be more "sticky" behaviors with consumers.

"We think that Google has a lot more optionality around their core business, particularly around what they're doing with artificial intelligence, machine learning, YouTube and the shift to mobile," Slingerlend said.

Meanwhile, businesses have increasingly told Slingerlend they plan to migrate more of their budget toward Amazon Web Services.

The volatility that rocked technology stocks earlier this year is not impacting business' plans to migrate to the cloud over the next five to 10 years, Slingerlend's research indicates. He adjusted Janus' portfolio to reflect the prediction that IT budgets will move increasingly away from legacy tech companies like Oracle and HP Enterprises and move toward firms like Workday and Salesforce.com.

"We think this is the inflection point for the shift to the cloud, and the legacy IT vendors have really been sitting on their hands," Slingerlend said. "They've been stockpiling cash, buying back stock, paying dividends, not investing in innovation."