Some investing decisions are easier than others. A high-growth stock with increasing profits at a low valuation could be a no-brainer buy. But if you take out the low valuation, it could become a real question. Similarly, investors might struggle to determine if a young, high-growth stock with an uncertain future is a better buy than a mature, lower-growth one that's well-established.

For most investors, the way to deal with the conundrum is actually quite simple. It's called diversification. Instead of choosing from these different types of stocks, buy both, and add a few more to round out your holdings. A solid group of stock picks should include proven, established winners that still have strong growth prospects.

One excellent example today is Amazon (AMZN -0.66%). If you weren't sure whether or not the e-commerce giant still has more growth ahead, consider what CEO Andy Jassy just said.

Is Amazon still a growth stock?

Amazon's revenue has increased by more than 10,000% over the past 20 years, or a compound annual growth rate of 26%. Its stock has gained nearly 5,000% over that time, and much more going back to its initial public offering.

During this time, it has expanded in multiple ways and become the unmatched e-commerce and cloud computing giant it is today. That began right at the beginning with a strong list of acquisitions that immediately set it apart as a leader in what was still the uncharted territory of e-commerce, and it continues to acquire other companies and launch new products and services in what is now a vast set of businesses.

While some of its innovations are major shifts -- such as its acquisition of One Medical last year that brings it into the healthcare industry -- many of them are minor improvements that strengthen its moat and ensure that no competitor can touch its lead. These might not seem revolutionary, but they're integral to Amazon's growth strategy.

There's still a long runway ahead

Jassy, who has been on every earnings call since he took over as CEO in 2021, provided shareholders with great news on the one last week. Sales were up by double digits, net income tripled from last year, and Amazon Web Services (AWS) is gaining momentum after a sluggish period, to note the highlights.

But what he said about the future might have been the most potent part of the update. Earlier this year, Amazon made a major shift in its delivery and fulfilment network. It moved from a national system to a regional one, with eight regions to serve different parts of the country.

The strategy involves keeping the most-popular products in all of those locations at all times, making it much faster and cheaper to get them to customers. Other products can still quickly move through channels to get to their destinations. Jassy said that delivery times are at their fastest in 29 years.

But this was the most potent part of the update: "We have a long way before being out of ideas to improve cost and speed." Since Amazon is so big, it takes time to make small changes happen. It also needs to test, test, test to get things right and have the right infrastructure at the right cost to make sure it ends up being cheaper and not more expensive.

The improvements it launched this year were likely a long time in the making. It has added multiple types of robots to its force. These use artificial intelligence and machine learning to sort and deliver with a high degree of automation and lower costs, while freeing up employees for more creative work. These are constantly upgraded with new technology.

Even minimal improvements make a big difference for Amazon's more than 200 million Prime members, who rely on it for essentials and other products. The faster it can get them their deliveries, the more loyalty and revenue it'll earn. And the cheaper it can do that, the more it can delight its shareholders with increased profits.

It's not just about fulfillment

Jassy's optimistic take really applies to the whole company. While he said it in reference to fulfillment, he gave plenty of updates about generative artificial intelligence and how it's transforming e-commerce, AWS, and advertising. Some examples are Amazon Bedrock, which allows AWS clients to customize large-language models with their own data, and Code Whisperer, which can write code for users based on company data. These are just early models of what should eventually grow into massive businesses and revenue drivers.

The are no guarantees in the stock market, but I wouldn't underestimate the amount of gas that Amazon has left in its tank.