We Fools are constantly on the hunt for winning stock ideas that we believe will generate strong returns for years on end. When we think we have identified a winning business, we like to buy it and hang on to it through thick and thin.

With that in mind, we asked a team of Fools to highlight a stock in their portfolio that they plan to hang on to for the ultra-long term. Read on to see why they picked Alphabet (NASDAQ:GOOG)(NASDAQ:GOOGL), Under Armour (NYSE:UA)(NYSE:UAA), and Starbucks (NASDAQ:SBUX).

An hourglass held between two hands.

Image source: Getty Images.

Alphabet will continue to benefit from digital browsing

Jamal Carnette, CFA (Alphabet): The market wasn't kind to Alphabet's recently reported fourth-quarter and full-year results. Overall, the company continues to post enviable growth rates for a company of its scale. Alphabet increased revenue 20.4% over the previous year's results; on a quarterly basis, it grew revenue 22.2% over last year's corresponding period. However, the company's fourth-quarter bottom line increased by only 8.3%, to $5.3 billion, as Alphabet's provision for income taxes increased by a massive 450% over last year's corresponding quarter, on account of a one-time tax adjustment. Still, the fickle market sold off shares to the tune of 2% because the company missed analyst expectations.

On a positive note, Alphabet confirmed that mobile search is one of its highest-growth areas. The biggest shift in internet browsing over the past five years has been from desktop to mobile, and that move benefits Alphabet, considering Google controls approximately 95% of the mobile-search market.

The company also continues to grow its advertising business. Earlier this year, a shocking report from Morgan Stanley analyst Brian Nowak found that 85% of every new dollar in online advertising was going to just two companies: Alphabet and Facebook. As the shift to online advertising continues, look for Alphabet to continue to post strong revenue growth rates.

Simply put, Alphabet's long-term thesis remains intact. The company is the largest digital advertiser and search engine in the world, and Alphabet will only continue to grow search and advertising revenue as internet usage increases from a combination of penetration and accessibility, while a push for digital advertising will boost the company's bottom line.

Still a believer in Under Armour

Brian Feroldi (Under Armour): The past six months haven't been kind to Under Armour's shareholders. The stock took a big hit in late October, after management ratcheted back its long-term growth targets. More recently, shares got crushed after the company reported sales growth of just 12% in the all-important fourth quarter. Not only was that figure far shy of management's guidance, but the company's CFO also resigned suddenly. That's a lot of bad news for investors to take in all at one time, so it was no surprise to see that shares took a big hit. 

However, a closer look at the quarter hints that investors shouldn't throw in the towel on this growth story just yet. While total sales growth was disappointing, the biggest culprit was slowing sales in North America. That's understandable, as the retail environment stateside was quite challenging for many retailers over the holidays. The recent bankruptcies of The Sports Authority, Eastern Mountain Sports, Sports Chalet, Golfsmith, City Sports, and Bob's Stores didn't help the matter, either. 

However, Under Armour's report did contain a handful of bright spots. Direct-to-consumer sales -- which bypass retailers altogether -- jumped by 23% and now account for nearly 40% of total sales. And footwear sales grew by a solid 36% year over year. Best of all, international revenue grew by 55% and now comprises 16% of total sales. These figures suggest that Under Armour's brand still remains strong.

While the company has some near-term challenges to overcome, I have a hard time believing that this growth story is dead. As long as founder and CEO Kevin Plank is at the helm, this is one stock I can't ever see myself parting ways with.

Middle-class people love their coffee, and there's about to be a lot more of them

Jason Hall (Starbucks): The global coffee giant's stock is down around 8% since first-quarter earnings came out in late January, and not without some justification. After all, Starbucks reported that traffic in its North American stores was pretty much flat in the quarter, a trend that started in 2016 and could continue through 2017. Furthermore, management indicated that it may feel the same way and is now projecting revenue growth between 8% and 10%, a reduction from original full-year guidance of 10% or greater at the end of the prior quarter. 

But Starbucks isn't the kind of company that will scare me away with a minor flattening of growth in its most mature market -- especially not right now. Starbucks' best days could be ahead of it, even as Howard Schultz steps down as CEO for the second time. 

To start with, Starbucks' growth opportunity in Asia is simply enormous. Within a decade, the middle class in China alone is likely to be double the size of the U.S., and Starbucks' management recently said it expects China to become the company's biggest market. Here's a little more context: At the start of 2017, Starbucks had nearly 16,000 stores in the Americas, versus fewer than 6,800 in the China/Asia Pacific region, with 2,500 of those in China. 

Bottom line: Growth very well could slow further -- or even stall -- in the company's more mature markets, but I won't sell. The global growth story is only getting started, and that's going to drive decades of growth. I'm not missing out on that.