Their clothing may be quite similar but these two stocks couldn't be more different.
First and foremost Cramer likes both of these high quality sports apparel companies. Both belong on your radar.
However, he says if you were to make your stock decision based on the latest earnings reports you may be tempted to swing for the fences with Under Armour.
Under Armour said it second-quarter net income more than doubled as consumers bought more of its athletic clothing and it expanded its shoe offerings. Results beat expectations and the company raised its revenue outlook for the year.
"By contrast, Nike delivered better than expected numbers but the upside surprise was modest," Cramer said.
Or if you're looking at innovation, again Under Armour seems like the better bet.
"On the earnings call, Under Armour pointed out that it's innovating like crazy," Cramer said. "They've rolled out new clothing that can battle the elements. They also have something called Cold Black, which is black apparel that reflects heat rather than absorb it. And the company has a new partnership with Marvel Entertainment and DC Comics to sell superhero branded apparel," Cramer said.
By comparison, Nike pointed out that they need to accelerate their innovation agenda.
If you didn't know any better you'd think game over. Fortunately Cramer knows better.
Valuations are anything but equal. "Nike sells for 18 times next year's earnings estimates with an 11% long-term growth rate, a totally reasonable valuation," Cramer said. "Under Armour sells for 37 times next year's numbers, which is very expensive, but reflects the company's 21% long-term growth rate.
Price action is also noteworthy. Shares of Under Armour have rallied almost 10% in the past 5 days and they climbed 12% in a single day after earnings. That suggests to Cramer that the stock is attracting mojo pros who play momentum stocks for growth.
"And eventually growth plays fall hard," Cramer said. That is, when growth begins to slow those pros cash out and put their money into the next growth story. "It could happen years from now but it's very much a factor in owning UA," Cramer said
Read More from Mad Money with Jim Cramer
3 mergers Cramer doesn't want you to miss
'This' earnings report really impressed Cramer
Are these stocks 'too dangerous' to hold?
Because it's currently a growth play, Cramer thinks it's more likely that Under Armour will advance rapidly, but he also thinks it's more likely to decline precipitously at some point in the future. By comparison, Cramer thinks Nike will advance more slowly but hold its gains.
Therefore, "If you're and older investor and you don't want to worry about the risk of a big miss, then I would still recommend buying Nike over Under Armour, despite Under Armour's stellar quarter," Cramer said.
"But if you're a younger investor with all the time in the world to make back any losses if Under Armour stumbles, then UA is the stock for you."
Call Cramer: 1-800-743-CNBC
Questions for Cramer? firstname.lastname@example.org
Questions, comments, suggestions for the "Mad Money" website? email@example.com