It's been a fantastic year on Wall Street. The S&P 500, Nasdaq Composite, and Dow Jones Industrial Average are up 24%, 24%, and 17%, respectively.

So, let's take a look at the three best tech stocks that investors should consider buying in October.

A stack of coins on top of many dollar bills.

Image source: Getty Images.

PayPal Holdings

For those in search of an affordable tech stock to buy in October, consider PayPal Holdings (PYPL -1.45%).

Unlike many tech stocks whose valuations are at multiyear highs, PayPal's current price-to-sales (P/S) ratio is only 2.8 -- significantly below its 10-year average of 6.5.

Granted, the company is in the middle of a turnaround, after shares plunged by more than 83% from its all-time high set in 2021.

Yet, there are signs that CEO Alex Chriss is righting the ship. As of its most recent quarter (the three months ending on June 30, 2024), PayPal's operating margin -- a key measure of profitability -- hit 17.5%. That's the highest level since 2021. And that's thanks to significant cost-cutting initiated by Chriss.

Moreover, PayPal's free cash flow per share -- another key indicator of financial health -- hit an all-time high of $6.23 last quarter. Nevertheless, PayPal stock remains well off its all-time highs.

In short, opportunity knocks: PayPal is a stock that long-term investors would be wise to consider.

Duolingo

The next tech stock investors should consider buying in October is Duolingo (DUOL -2.50%).

Simply put, Duolingo is a hypergrowth stock. The company's trailing 12-month revenue stands at $634 million. That's up 87% from $339 million two years ago. Indeed, the company averaged an astounding quarterly revenue growth rate of 43% during that period.

The company's rapid growth is all due to the popularity of its language-learning application. As of its most recent quarter (the three months ending on June 30, 2024), Duolingo reported 100 million monthly active users (MAUs) and more than 8 million subscribers.

What's more, many of those active users are extremely active. The company noted that about 20% of its daily active users (DAUs) -- roughly 6 million people -- have daily learning streaks of greater than one year.

Those fantastic user numbers are important because they indicate that the company is growing and retaining users, which are its key growth engine. As more users join and engage with the platform, Duolingo can further monetize them, primarily by turning them into paid subscribers.

Moreover, the company holds a truly global appeal, as people of all ages and backgrounds are often interested in mastering a foreign language.

Duolingo is a stock long-term growth investors should keep an eye on.

Palantir Technologies

Finally, there's Palantir Technologies (PLTR -3.72%).

Look, I've been bullish on Palantir for a long time. So, it's satisfying to see that the stock is up 141% over the last year.

Moreover, despite its incredible run, I don't think Palantir is done. Not by a long shot.

Here's the deal. Palantir is one of the first companies in an emerging sector: artificial intelligence solutions. At the moment, the field is so new that most of the stocks people associate with AI are the hardware companies: Nvidia, Advanced Micro Devices, and Taiwan Semiconductor Manufacturing.

However, as the AI revolution rolls on, the next big wave will be in how to apply its immense power to practical applications. That's why Palantir remains a smart long-term investment.

The company is positioned to help large organizations (governmental, non-profit, and commercial) leverage the power of AI to improve their operations.

In addition, this is an effortlessly scalable business. Palantir can -- and is -- already growing its customer count and revenue by leaps and bounds.

For example, in its most recent quarter (the three months ending on June 30, 2024), the company announced annual revenue growth of 27%, with its overall customer count growing 41% year over year.

Palantir is riding a wave of surging AI demand and remains a must-know stock for growth-oriented investors.