Broadridge's data, then, represent a significant paradigm shift.
The past year saw $267 billion in ETF assets sold through independent and wirehouse broker dealers, registered investment advisors and discount brokerage firms. That compared with $255 billion in mutual funds, which still saw total assets grow 10 percent though that gain was led more by institutional than retail investors, according to Broadridge.
Read MoreDoes your advisor stand out from the crowd?
"ETFs have become a bigger part of the pie and reasonably adopted by individuals as well as advisers," said Frank Polefrone, senior vice president at Broadridge. "A few years ago there were probably more questions about ETFs and that seems to have gone by the wayside,"
Indeed, despite their liquidity, lower cost and tax advantages, ETFs still have critics.
Prominent among them has been Vanguard founder Jack Bogle, who is perhaps the financial world's strongest supporter of index funds—the leader of the "Bogleheads"—but not a backer of ETFs, even though most of them track broad market measures like the S&P 500 and are similarly passive in nature. (Only 15 percent or so of mutual funds are passive.)
However, since Bogle relinquished his formal duties as head of the company, Vanguard has become a leader in the ETF industry. Vanguard currently ranks second among all providers, with $470.4 billion of its total $3.1 trillion under management dedicated to ETFs, according to ETF.com.
Read MoreRobo firms gain traction with financial advisors
"Just because you can trade them in the middle of the day doesn't mean you have to trade them in the middle of the day," said Jim Rowley, senior investment analyst at Vanguard. "They're actually funds—pooled investments that buy portfolios to give investors diversified portfolios for securities at reasonably lower costs and can be used in a buy-and-hold manner."
Rowley called the preference for ETFs "a very positive thing for Vanguard."
Still, the big investment advisory firms are reluctant to play favorites, despite the sharper growth rate for ETFs. Mutual funds still generate the bigger fees, though retail investors have begun to recoil against their costs and are demanding more ETFs.
Charles Schwab, which is the seventh-largest provider in the ETF space with $32.4 billion under management, has gotten considerably more aggressive with its offerings.
"We firmly believe that mutual funds and ETFs will continue to play an important and prominent role in investors' portfolios," a Schwab spokesman said in a statement to CNBC.com. "They both provide tremendous benefits as part of a diversified portfolio."