Better Buy: NIKE, Inc. (NKE) or Under Armour Inc (UA)?

Ever since Under Armour Inc (NYSE:UA) CEO Kevin Plank founded his company in 1996, he’s held the industry dominance of NIKE, Inc. (NYSE:NKE) squarely in his sights. Plank even used to send a Christmas card every year to Nike founder Phil Knight that read, “You will hear about us one day.”

In fact, during one memorable exchange at a football game between Under Armour Inc (NYSE:UA)-sponsored University of Utah and NIKE, Inc. (NYSE:NKE)-clad University of Oregon, Plank asked Knight if he wanted to make a bet on the game.

Knight only turned, and replied with a smile, “I think we already have.”

Two market-beaters
So far in 2013, both Under Armour Inc (NYSE:UA) and NIKE, Inc. (NYSE:NKE) stocks have handily outperformed the otherwise respectable 17% return offered by the S&P 500:

NKE Total Return Price data by YCharts.

That raises the question: Which is the better stock for investors to buy now?

Everyone likes an underdog
While Under Armour Inc (NYSE:UA) has embraced the role of being the little guy so far, its stock has more than tripled over the past five years. As a result, Under Armour’s current market capitalization at nearly $7 billion has finally pushed the budding company out of mid-cap territory and into the big leagues. What’s more, shares of Under Armour admittedly look expensive as they trade hands at more than 55 times last year’s earnings, and 35 times next year’s estimates.

Still, looks can be deceiving, and there’s a reason Under Armour Inc (NYSE:UA) has long stood out as one of my favorite stocks.

So how much more can Under Armour possibly grow? Despite increasing year-over-year revenue by at least 20% each quarter for the past three years, Under Armour management continues to stand by their long-term goal of maintaining that 20% growth for the foreseeable future.

And while the stock might still look a bit rich — even with that growth — investors have every reason to believe Under Armour Inc (NYSE:UA) is only just getting started, as international revenue only accounted for 6% of last year’s sales. Of course, that’s not lost on the company, and recent quarters have seen a significant push by Under Armour executives to further develop their international business.

In addition, as I noted last month, UA’s footwear revenue rose 43% last quarter from the year-ago period to $45 million, so it appears the company’s success in apparel should be able to translate to the multibillion-dollar footwear market — and remember, Under Armour only began making shoes in 2006.

The case for the industry stalwart
So why might you want to buy shares of NIKE, Inc. (NYSE:NKE)?

Relative stability, for one. Though Under Armour Inc (NYSE:UA) may have outperformed Nike stock since the smaller company’s IPO in November 2005, investors may have needed an airsickness bag to really enjoy those gains:

NKE Total Return Price data by YCharts.

By contrast, folks who held Nike stock over the same period enjoyed a much steadier climb.