Although value stocks have been the better ultra-long-term investment opportunity, in comparison to growth stocks, the past decade has belonged to high-growth companies. The persistent low-interest rate environment has given high-growth businesses an opportunity to borrow at a low cost, thereby fueling top-line sales increases. With the Federal Reserve seemingly intent on keeping rates low for the foreseeable future, this might mean the good times are here to stay for growth stocks.

The big question, of course, is what growth stocks you should own as we drive headlong into a new year (and decade). After scouring the market, the following mix of large-, mid-, and small-cap growth stocks should help to fatten up your portfolio by year's end.

A businessman holding a potted plant in the shape of a dollar sign

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Intuitive Surgical

Robotic-assisted surgical system developer Intuitive Surgical (NASDAQ:ISRG) certainly isn't going to be turning value investors' heads at 42 times its forward-year earnings, but it's a pretty hard company for growth investors to overlook considering its monumental competitive advantages.

For one, this is a company that keeps getting stronger as it ages, primarily due to its razor-and-blades business model. Though Intuitive Surgical's da Vinci systems are pricey (ranging from $0.5 million to $2.5 million), the margins associated with these surgical systems tends to be modest. After all, these are intricate and costly systems to develop and manufacture. Rather, the instruments and accessories sold with each procedure, and the servicing done on each of its installed systems, is where Intuitive Surgical makes bank. These high-margin "blades" will continue to grow as a percentage of total sales as the company's installed base of da Vinci systems (the "razor") increases.

Also consider that Intuitive Surgical's da Vinci system has a long growth runway ahead of it. Already a dominant force, in terms of market share, for urology and gynecology surgeries, management expects to gobble up significant market share in thoracic, colorectal, and general soft-tissue surgeries in the years to come. Given that healthcare companies are highly recession-resistant, Intuitive Surgical looks to be a no-brainer stock to own in 2020.

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Image source: Pinterest.

Pinterest

I've said it before, and I'll say it again. If you missed out on Facebook and have been kicking yourself as an investor, Pinterest (NYSE:PINS) is going to give you a chance to redeem yourself.

Pinterest may not have the ad-pricing power of Facebook, but all of its important metrics are headed in the right direction. Monthly active user count increased by 71 million at the end of September to 322 million from the prior-year period, with the bulk of this increase coming from international markets, which registered 38% year-on-year user growth. 

Speaking of international markets, Pinterest's efforts to monetize overseas users has been paying off, as evidenced by the more-than-doubling in year-over-year average revenue per user of $0.13, compared to $0.06 in the prior-year quarter. The company's emphasis on video, which has been shown to improve user engagement, and its expansion of shoppable products on the site, are clearly paying off domestically and abroad. With Pinterest likely to turn profitable in 2020, now is the time to own a piece of this popular social media site.

Four vials of cannabinoid-rich oil lined up on a counter

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MediPharm Labs

Although marijuana was nothing short of a nightmare investment in 2019, we could see certain niches within the industry do a lot of growing up in 2020. That's why extraction-services provider MediPharm Labs (OTC:MEDIF) deserves consideration for your portfolio.

MediPharm should turn a lot of heads this year given that it's at the center of the high-margin derivatives movement (derivatives being alternative pot products, such as edibles, infused beverages, and topicals). MediPharm processes hemp and cannabis biomass to yield the resins, distillates, concentrates, and targeted cannabinoids that growers use to create derivatives. With these alternative products launching in Canada a little over three weeks ago, growers are likely to devote a substantial portion of their portfolios to these higher-margin products.

Additionally, MediPharm Labs has already produced back-to-back quarters of no-nonsense profits (i.e., without a number of one-time benefits or adjustments). The company's fee-and-volume-based processing contracts are often 18 months or longer, providing the ability to forecast expenses and cash flow with reasonable accuracy, and thus allowing MediPharm to kick out profits. With the sales forecast to rise by 60% in 2020, MediPharm could continue to show shareholders the green.

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Livongo Health

There are a number of healthcare trends that could deliver big-time growth in 2020, but I have my eye on diabetes as a long-term high-growth indication. Roughly a third of all Americans have diabetes or prediabetes, and simply maintaining positive health habits is arguably the biggest hurdle for these folks. That gives Livongo Health (NASDAQ:LVGO) an opportunity to be a disruptor in this space.

Data-driven Livongo offers a handful of wirelessly connected devices that have been shown to help diabetics and prediabetics by providing actionable tips to improve their health. In just one year, we've seen Livongo's patient count more than double to 208,000, suggesting that its actionable advice is resonating with users.

More importantly, Livongo Health's platform is built as a subscriber model. Subscription models typically see less patient churn when economic "hiccups" occur, and they provide highly predictable revenue and cash flow that the company can use to plot out of its growth strategy without producing jaw-dropping operating losses (remember, Livongo is still in the early stages of its growth and is losing money).

A businessman touching a digital image of a cloud, which is wirelessly connected to multiple other devices

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Amazon

Last, but certainly not least, it's become impossible to ignore Amazon's (NASDAQ:AMZN) dominance in e-commerce or cloud computing.

Pretty much everyone is aware of Amazon's impact in the e-commerce space. According to eMarketer in June, Amazon would be responsible for 38% of all e-commerce sales in 2019, and its Prime membership is doing an excellent job of keeping people within its ecosystem. But the real superstar here is Amazon Web Services (AWS).

The company's cloud services platform is growing more than twice as fast as its e-commerce operations, and the margins for AWS are light years ahead of every other business segment. Through the first nine months of 2019, AWS was responsible for $6.6 billion in operating income on "only" $25.1 billion in sales, which compares to $4.1 billion in operating income on $168 billion in net sales for all of its other business segments. Similar to Intuitive Surgical, Amazon's business is only getting stronger as AWS become a larger percentage of total sales. This makes Amazon and its historically low PEG ratio a standout for growth investors.