U.S. companies stand to reap a "huge benefit" from the new Republican tax law, which includes a dramatic corporate rate cut, said the head of portfolio strategy at Merrill Lynch Wealth Management.
"We're anticipating at least earnings going up an additional 10 percent than where we were without the tax plan," Mary Ann Bartels told CNBC's "Squawk Box" on Friday. "We were already seeing analysts raising their numbers. And now with the tax plan, we expect the numbers to go up even more."
As part of the tax law, the federal corporate tax rate was cut from 35 percent to 21 percent.
Expectations for strong earnings have helped propel the stock market to one of its best yearly starts in years, Bartels said.
Credit Suisse's chief U.S. equity strategist, Jonathan Golub, agrees with Bartels about the tax benefit to earnings and the market.
"About 25 companies have provided guidance on what's going to happen to their tax rate," Golub said in a later CNBC interview on Friday. Their earnings-per-share estimates for 2018 are "up 9 percent from the day before the tax change up until today," he said.
"For those companies who provided no guidance at all, they're up only 1 percent on their EPS" 2018 estimates, he said. "The EPS estimates are way too low; probably 7 or 8 percent more upside to 2018 EPS as that guidance trickles out."
However, Tracie McMillion, head of global asset allocation strategy at the Wells Fargo Investment Institute, does not think the tax boost to the market will last.
The market rally in the first few weeks of 2018 has been a "rapid repricing" due to tax reform, said McMillion, who appeared with Golub on "Squawk on the Street." "We don't expect that rate of return to last through the rest of this year. We see some leveling off."
The Dow Jones industrial average hit its 10th all-time intraday high of 2018 on Thursday, but ended up closing nearly 100 points lower.
The Dow has gained more than 5 percent so far this year, on top of a 25 percent advance for all of 2017. Since Donald Trump won the presidency in November 2016, the Dow has rocketed nearly 42 percent higher as of Thursday's close.
Bartels also credits a stronger U.S. economy and recoveries in emerging markets, Japan and Europe. "We're kind of what I call in the sweet spot of this part of the growth in the economy and in the world."
However, earlier this week, billionaire investor Sam Zell and sovereign wealth fund advisor Komal Sri-Kumar told CNBC that they believe the stock market rally is showing signs of "irrational exuberance." They were evoking then-Federal Reserve Chairman Alan Greenspan's famous December 1996 "irrational exuberance" speech that had asked tough questions about the strong market environment at the time. About three years later, the dot-com bubble burst in 2000.
But Bartels told CNBC on Friday that she does not see any "irrational exuberance" in the market.
Bartels also sees the stronger economic backdrop and the new tax law leading to more acquisitions.
"We think you're going to get the return of M&A too," she said, predicting mergers on a smaller scale, not necessarily the big headline-grabbing deals.
As for her favorite sector right now, Bartels said, "The true leadership in this market is technology."