Are you new to investing, or just want to make sure your portfolio has a solid foundation? There are some stocks that work better than others when it comes to building a solid portfolio that will perform well for decades to come without excessive risk. Here's why three of our contributors think you should take a closer look at Berkshire Hathaway (NYSE:BRK-A) (NYSE:BRK-B), Activision Blizzard (NASDAQ:ATVI), and (NASDAQ:AMZN).

A massive investment portfolio in one stock

Matt Frankel, CFP (Berkshire Hathaway): If you're looking to build a solid foundation for your portfolio, I can't think of any better candidate than Berkshire Hathaway, the conglomerate led by legendary investor Warren Buffett.

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If you aren't familiar, Berkshire's core business is insurance, which it operates through its wholly owned GEICO subsidiary and some huge reinsurance operations. In addition, Berkshire owns dozens of other businesses, including household names such as Duracell, Clayton Homes, Fruit of the Loom, Pampered Chef, and many others. Berkshire has operations in a variety of businesses, ranging from auto dealerships to private jets.

In addition to its subsidiaries, Berkshire also owns a massive stock portfolio worth over $200 billion. It contains over 40 different stock positions, including very large investments in Apple, Bank of America, American Express, Wells Fargo, and Coca-Cola. Warren Buffett is still the portfolio's primary investment manager, and most of the larger investments were chosen by Buffett himself.

In short, Berkshire offers a diverse investment portfolio, much of which was hand-selected by the greatest investor of all time, all in a single stock. I've written before that if I could own just one stock, it would be Berkshire, and the reason is that although it's one stock, it's far more than just one business. And, Berkshire has a fantastic track record of delivering market-beating returns for shareholders.

A leader in interactive entertainment

Keith Noonan (Activision Blizzard): Video games have come a long way over the last couple decades, and it's a safe bet that interactive entertainment will continue to become more popular over the next 50 years. Activision Blizzard has been a consistent leader in the industry, and the company stands a good chance of maintaining a forefront position and delivering strong performance over the long term.

Known for franchises like Call of Duty, World of Warcraft, and Overwatch, Activision Blizzard has seen a bit of a shake-up over the last year -- and shareholders have had to weather some turbulence. The company's stock is down roughly 33% over the last year due to slowdown for some of its key franchises and a broader sell-off for video game stocks.

The market seems to have overreacted to the cyclical decline of some of the company's properties and interpreted the success of competing, free-to-play games like Fortnite as a permanent destabilizer rather than a catalyst for expanding the market. Competition will always present a risk factor, but the video game industry is still growing and can support numerous winners, and Activision Blizzard stock is trading at an opportune price.

The company is bridging franchises including Call of Duty and Diablo to mobile platforms, paving the way to reach millions of new gamers and expand the reach of its properties in fast-growing markets like China and India. With long-term growth opportunities in potentially explosive categories like esports and the potential to further leverage its gaming hits with tie-in merchandise and other forms of media, the company has expansion avenues outside of its core gaming business as well.

Activision Blizzard also pays a dividend, and while its yield doesn't look like much at 0.8%, the company has raised its payout for eight years straight and increased the size of its annual distribution by nearly 150% over the stretch. Shares trade at roughly 21 times this year's expected earnings, and for long-term investors looking for significant exposure to the video game industry, Activision Blizzard is a stock worth building a portfolio around.

The e-commerce giant with plenty of irons in the fire

Chris Neiger (Amazon): When looking for companies that have sustainable competitive advantages, it hardly gets better than Amazon. What company can claim that about half of all e-commerce sales in the U.S. happen on its platform, that it has the largest cloud computing market share in the industry, and that it's quickly becoming a major digital advertising player? Only Amazon, that's who.

Of course, the company's e-commerce dominance gets most of the attention, and it's what brings in the most sales for Amazon. The company now has more than 100 million members subscribed to its Prime service -- which includes free two-day shipping and other goodies like free video and music content -- and those customers are helping to fuel more sales. A Prime member spends about twice the amount as a non-Prime member on Amazon's site.

While Amazon's e-commerce business is humming along nicely, the company's biggest profit generator right now is its Amazon Web Services (AWS). AWS is Amazon's cloud computing company and holds about 32.3% of the market, with Microsoft taking the No. 2 spot with just 16.5%. The great news is that the cloud computing market is just getting started and is on pace to become a $278 billion one by 2021.

If all of that weren't enough to entice investors, Amazon is also quickly rising as a major digital advertising player as well. The company took about 4% of the digital ad market in the U.S. last year, but that percentage is expected to grow to 7% by 2020. In the coming years Amazon's advertising business could become even more lucrative than its AWS business, with some estimates putting Amazon's ad business at $16 billion in operating income by 2021 compared with $15 billion for AWS.

Whether it's Amazon's large e-commerce business, its lead in the cloud computing market, or its growing potential to benefit from advertising, investors have their pick of reasons why this company is worth building their portfolio around.