Call it the investment equivalent of dogs and cats living together.

Stocks and have been winners in 2015, but according to one major player, stocks will prevail as the better investment this year.

On Tuesday's "Futures Now," BlackRock's chief investment strategist for fixed income, Jeff Rosenberg, said that if he were to take a bet on stocks or bonds in 2015, he'd pick stocks.

"I'd be a buyer of the stock market, just because the risk and reward," he said. "The issue with bonds right now is there's a skew to the potential returns. The upside is quite limited, given how low yields are." The yield on the U.S. 10-year has stayed below 2 percent for the better part of the year, currently resting at 1.9 percent. "The difference with the stock market is there's a more balanced risk and reward in terms of the upside versus the downside."

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Rosenberg, who correctly called for the stock market to outperform the bond market in both 2013 and 2014, said that investors will continue to see a tight correlation between stocks, bonds, currencies and commodities through the end of the year.

"Everything has been highly impacted by global monetary policy," he said. "So I think they're both going to move, and they're both going to be highly impacted not by what we've already seen. That's been the story that's gotten us to this point; that's weak economic data, but how is the data going to turn and progress."

According to Rosenberg, weak economic data in the first quarter was seasonal, and the economy could see a pickup in the second half of the year. "When you see the economic data change, the narrative around the bond market and the stock market will change at the same time."

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Typically, when economic activity picks up, investors chose risk assets such as stocks over bonds. But this year, the bond market has a couple of things working for it: low inflation and extreme low rates in Europe. The German 10-year bond is yielding close to zero, almost 200 basis points less than Treasurys, which are viewed as the ultimate safe haven.

However, despite low rates in Europe, Rosenberg sees a combination of an improving economy and a potential Fed rate hike in September as catalyst for a bond sell-off.

"The theme [for a Fed hike] is really all about the pace," he said. "My central case is around September and then another increase probably in December."

With so little upside in bonds, Rosenberg sees greater opportunity in stocks.

"In terms of what the skew is to your return profile, stocks are favored."