Without a doubt, buying and holding great stocks for the long term is the best way to predictably generate wealth. But it can be exceedingly difficult to weed out which stocks are worthy of your long-term dedication.

So we asked three top Motley Fool contributors to each find a stock investors can comfortably hold for the next two decades. Read on to learn why they chose Markel (NYSE:MKL), Nike (NYSE:NKE), and Alphabet (NASDAQ:GOOG)(NASDAQ:GOOGL).

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IMAGE SOURCE: GETTY IMAGES.

This stock can keep climbing indefinitely

Steve Symington (Markel): Markel might look expensive trading at nearly $1,200 per share. But in light of its latest quarterly report last week, we know that the stock technically trades at a reasonable 1.7 times book value. Given Markel's diversified approach to creating long-term shareholder value, there's also no reason to believe its value can't continue increasing for decades to come.

To start, Markel's investing operations have served as a key point of near-term weakness in recent quarters given recent market volatility. But putting aside the fact that the equity portion of that portfolio has more than tripled in value over the past five and half years, Markel's co-CEO -- and world-renowned value investor -- Tom Gayner noted that they view that volatility as a "chance to purchase wonderful long-term businesses at attractive prices."

Second, in the meantime, Markel has been able to lean on the relative strength of its profitable specialty insurance businesses, as well as its diversified noninvesting, noninsurance group of acquired businesses operating under the Markel Ventures segment. The latter group covers everything from bakery equipment to car-transport trailers and ornamental plants.

Of course, the similarity of this approach to the company Warren Buffett built is why Markel is also prominently known as a "mini-Berkshire Hathaway." But considering Berkshire is more than 30 times larger than Markel as measured by market capitalization as of this writing, I tend to favor Markel's chances for achieving outsized growth over the next 20 years.

A marathon rather than a sprint

Demitri Kalogeropoulos (Nike): Investors have pushed Nike's stock to new highs recently, following news that the company's short-term rebound plan is finally gaining steam. But there are even better reasons to be optimistic about the sports apparel giant's long-term results.

While the consumer shift toward e-commerce shopping hurt Nike's profits over the past two years, it's likely to have a positive impact on its earnings going forward. Direct sales are far more profitable than sales that the company makes to its retailing partners after all. That helps explain why executives are pouring resources into the digital channel today as more than just a means to protect against shrinking customer traffic at sports apparel retailers.

Meanwhile, Nike has a firm foothold in emerging markets, and executives expect China alone to reach 10 times the addressable market of the U.S. between now and 2030.

Finally, the company spent $3.6 billion marketing its products last year, up 7% from fiscal 2017. That hefty outlay might seem like a liability, but it amounts to a massive competitive advantage that should serve the brand well in the years to come. Rivals can't match that marketing and advertising commitment, after all, and so Nike's brand is should continue to rank among the most valuable in the world.   

A winner for today and for the future

Keith Speights (Alphabet): Some things that we do and use today will probably still be around 20 years from now. Other things will be radically different. There's one company that I think will benefit tremendously from both of these scenarios: Google parent Alphabet. 

Let's start with things that are likely to still be in heavy use two decades into the future. I'd say it's a pretty safe bet that the internet isn't going away. Sure, it might change a lot, but people all over the world will still be connected. That means there will probably be a tremendous need to search the internet. And Alphabet's search applications, led by the Google search engine, are likely to remain at the top, generating billions of dollars in advertising revenue for the company.

But what about things that might change? Many experts predict that self-driving cars will be widespread in the future. Greater use of artificial intelligence (AI) applications is almost a certainty. Personalized medicine could change how healthcare is delivered. Alphabet is a pioneer in all of these areas. 

The stock isn't just a potential winner 20 years from now, though. Alphabet is doing pretty great right now, as its fantastic second-quarter results show. I predict that the company will have plenty of quarters just as good between now and 2038.

The bottom line

We obviously can't guarantee that these three companies will go on to deliver enviable returns for investors who buy today -- a lot can happen in 20 years. But whether we're talking about Markel's diversified, scalable business model, Nike's focus on direct sales and global growth, or Alphabet's core internet industry leadership and supplemental other bets, we think chances are high that they'll each survive and thrive in that time. And we believe astute investors would do well to own a piece of each business for the long run.

Suzanne Frey, an executive at Alphabet, is a member of The Motley Fool's board of directors. Demitrios Kalogeropoulos owns shares of Berkshire Hathaway (B shares) and Nike. Keith Speights owns shares of Alphabet (A shares). Steve Symington owns shares of Markel. The Motley Fool owns shares of and recommends Alphabet (A shares), Alphabet (C shares), and Markel. The Motley Fool recommends Berkshire Hathaway (B shares) and Nike. The Motley Fool has a disclosure policy.