Despite a bumpy road riddled with trade tensions, rate hike drama and global growth fears, stocks are pacing for their best first half in 22 years and are hovering near record levels.

With just three more trading days left in June, the has rallied more than 17% in 2019, pushing the SPDR S&P 500 ETF to new highs. ETF inflows remain positive but choppy — and are slowing down significantly from a year ago.

Average monthly inflows have fallen from $30 billion to closer to $10 billion — a rate Nick Colas from DataTrek Research said will be the new norm.

"We're not going to have this monster growth that we had in the middle part of the decade," Colas said Monday on CNBC's "ETF Edge." "It's just going to be slower and more organic."

And so far, the U.S. has seen total inflows of roughly $68 billion — about half of what we saw by this time last year, according to ETF.com — slowing but still growing.

Still, the ETF business has had some notable winners this year — and it's a fairly diverse group leading the charge.

Top-performing ETFs in 2019 (excluding leveraged and inverse ETFs):

Clearly, the momentum trade has been big this year — a trend that Colas sees carrying over into the second half.

"I see momentum as being a big theme," he said. "And then a bit of 'dash-for-trash' with some of these third-tier emerging markets that just got very depressed and now, with rates coming down, are beginning to lift again."

But these big winners won't necessarily set the same tone for the rest of the year. Keep in mind, the best-performing ETF in the first quarter was the ETFMG Alternative Harvest ETF. The cannabis play bounced back from a steep sell-off in the fourth quarter and has been holding up but trading sideways ever since.

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