I could pretty easily rattle off the names of at least 20 stocks that I think will be long-term winners. But if you asked me to narrow the list down to just the top three, it would take me a while to respond. And if you wanted to choose just one stock, I'd be frozen in analysis paralysis for longer than you'd want to wait.

However, I have been thinking quite a bit about what that one stock would be. I've admittedly gone back and forth multiple times, going with one stock first then opting for another. But after mulling and contemplating for way too long, I made a decision.

The one stock I'd buy right now is... Amazon (NASDAQ:AMZN). There are three primary reasons why I picked the e-commerce giant.

Lght bulb over a woman's palm and money shaped into a dollar sign over a man's palm

Image source: Getty Images.

Playing defense

Like many investors, I suspect that the nice stock market rebound we've enjoyed in recent months could fizzle. We've already seen some signs of this beginning to happen, although it's still too early to know for sure. While I have a long-term perspective when it comes to investing, it's still no fun to buy a stock that could be likely to soon go down -- even if only temporarily.

The bottom line is that I'm playing defense somewhat right now. I'd like to keep cash on hand to buy stocks on the dip if I'm right that the market could slide even more. However, my view is that Amazon is actually a pretty good defensive stock to buy in the current environment. 

Is Amazon completely immune to another market sell-off? No. The stock fell more than 20% earlier this year with the uncertainty about the COVID-19 outbreak. But Amazon has proven to be quite resilient in the wake of the pandemic. Consumers buy more online when they're at home more, and Amazon.com benefits from it. Amazon Web Services profits as businesses expand their cloud operations to beef up their online presence.

COVID-19 still presents the biggest risk to the stock market. I think that Amazon is one of the best stocks to buy with the ongoing threat from the economic effects of the coronavirus disease.

A moat as wide as the Amazon itself

Over the longer term, companies will face significant threats other than the COVID-19 pandemic. The biggest risk is failing to stay ahead of competitors. That leads me to the second main reason I chose Amazon as my top stock: The company has a moat as wide as the river it's named after.

There are several ways that companies create moats for their businesses. Cost advantages, network effects (i.e., their products and services become more valuable as more customers use them), high switching costs, brand recognition, and strong intellectual property rights are some of the most important ones. Amazon's moat includes pretty much all of these.

I could go on and on with examples about the different ways that Amazon has built a formidable moat, but I'll instead just focus on one example: Amazon Prime. It's one of the "stickiest" services around. Once a consumer enrolls in Prime, they're more likely to buy more products through Amazon. The more items purchased through Amazon, the greater its purchasing power and attraction to third parties wanting to join its ecosystem. 

A $1.3 trillion growth machine

Last, but definitely not least, Amazon still has tremendous growth opportunities. Normally, I'd say that a massive company will have a harder time generating growth than a smaller company would. But Amazon isn't a normal company. 

Amazon delivered 23% year-over-year revenue growth and 41% earnings growth in the first quarter of 2020. That's not just a one-off fluke. The company has multiple avenues for keeping its remarkable growth streak going.

E-commerce is obviously an important example. Cloud services is another. I expect Amazon will enter and dominate more markets in the not-too-distant future, with healthcare at the top of the list

Don't be surprised if Amazon emerges as a major rival to the big pharmaceutical chains over the next few years. Don't be shocked if it competes in the telehealth market. Leveraging its artificial intelligence expertise to build healthcare applications is another real possibility, in my view.

There are plenty of great growth stocks . As I stated earlier, I could easily name quite a few that I like. But Amazon's a rarity -- a $1.3 trillion growth machine. The company's growth prospects, combined with its resilient business model for times like these and its exceptionally strong moat, make Amazon especially attractive right now. 

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.