What will the stock market do next? Many have ideas and opinions, but the truth is that no one knows the answer to this question for sure. What we can be confident about, though, is that the stocks of companies with solid business models and significant growth opportunities should outperform the overall market over the long run.

There are plenty of stocks that meet these criteria and present attractive opportunities for investors. Here are three growth stocks I'd buy right now.

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1. Alteryx

In my view, the best stocks to buy are those of companies that are growing fast, have a huge addressable market, and have a clear competitive advantage that should enable them to capture a big chunk of that market. Alteryx (NYSE:AYX) checks off all of these boxes.

Alteryx provides a cloud-based software platform that enables quick and easy analysis of large amounts of data. Analysts don't have to write programs or manually enter data into spreadsheets. Alteryx's software takes care of pretty much everything. 

The company's sales skyrocketed 65% in 2019 and jumped 43% year over year in the first quarter of 2020 even with a negative impact from the COVID-19 pandemic in March. But even with this impressive growth, Alteryx still claims less than 1% of its $49 billion addressable market.

Customers choose Alteryx because its platform simplifies and speeds up data analysis. And increasingly more large customers are jumping on board: Alteryx's customer base includes 37% of the Forbes Global 2000, the biggest 2000 public companies in the world. 

2. The Trade Desk

The Trade Desk (NASDAQ:TTD) operates in a completely different market than Alteryx does. But it also is growing fast with a massive potential market and a compelling competitive advantage.

Advertising is undergoing a transformation. The back-and-forth negotiations between ad agencies and media outlets of the past is rapidly giving way to software-driven programmatic ad buying. This programmatic ad model is much faster and more cost-effective for ad buyers. The Trade Desk's software is the clear leader among buy-side programmatic ad platforms.

The Trade Desk delivered 33% year-over-year revenue growth in Q1 despite the COVID-19 outbreak affecting ad spending at the end of the quarter. Although the company's near-term prospects could dim somewhat with the ongoing impact of the pandemic, The Trade Desk's long-term outlook remains very bright.

By 2025, the total global advertising market is expected to reach close to $1 trillion. Programmatic advertising is only $34 billion of that total right now, but it's growing fast. The rising adoption of connected TV is also boosting digital advertising demand, with all forms of video potentially capturing half of the $1 trillion total ad market. The Trade Desk is well-positioned to profit from both of these trends.

3. Zscaler

While many companies are being hurt by the COVID-19 pandemic, Zscaler (NASDAQ:ZS) could actually benefit. Its cloud-based security platform is ideal for enabling employees working from home to securely access corporate applications and data. And there are a lot more people working from home these days.

The company's revenue jumped 36% year over year in its fiscal 2020 second quarter. Zscaler should be able to generate a similar level of growth in the rest of the fiscal year. But it's the company's long-term prospects that are especially attractive.

Zscaler is disrupting a $20 billion addressable market. This market should expand significantly over the next decade with the major shift of apps and data to the cloud. But does Zscaler have a competitive edge to be able to capture a lot of this growth? I think so.

It's the only security vendor certified by Microsoft for the popular Office 365 application suite. The increased adoption of Office 365 gives Zscaler a major growth opportunity all by itself. Zscaler's security platform was also designed from the ground up to support cloud security while its rivals have legacy technology. The market is big enough for multiple winners. I fully expect Zscaler to be one of them.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.