Apple (NASDAQ: AAPL) and Nvidia (NASDAQ: NVDA) are the two most valuable companies in the world. Their market caps are each well over $3 trillion, and it may only be a matter of time before there's one worth $4 trillion. It could potentially happen within the next year.

The likelihood is high that the first stock to reach that pinnacle will be one of these two tech giants. But will it be Apple or Nvidia? Which looks to be the better buy from here on out?

The case for Apple

The advantage Apple has in reaching $4 trillion first is that as of last week, it had a higher market cap than Nvidia -- nearly $3.7 trillion versus $3.4 trillion for the chipmaker. But that's not the only reason Apple might get there first.

Right now, Nvidia has been experiencing mammoth growth due to artificial intelligence (AI) because many tech companies rely on its high-performance chips for AI-related development. But other companies are developing their own chips, which could provide competition for Nvidia down the road.

Apple, for instance, has been using chips from Amazon to help develop its AI models. Meanwhile, China has recently launched an antitrust probe into Nvidia, which could affect its long-run growth opportunities in that market. As well as Nvidia has been performing of late, there could be challenges that weigh on the business in the not-too-distant future.

Apple, on the other hand, may soon get a significant boost from AI as it adds it to more features on its phones. The company has announced Apple Intelligence, but many new features, including enhanced Siri capabilities (like editing a photo, extracting a PDF from an email), won't be available until the new year.

As those features roll out, they could generate interest on social media and result in more phone upgrades and revenue growth for the business. If that happens, that may be enough to send the stock to a $4 trillion market cap.

The case for Nvidia

Nvidia's stock has rallied more than 330% over the past three years, prompting many investors to worry about whether it may be approaching a peak. But when you consider the impressive results the company has generated, its valuation isn't all that outlandish.

Based on analyst projections, Nvidia is trading at a forward price-to-earnings multiple (P/E) of 33, which is only slightly higher than Apple's premium. But while the iPhone maker has been growing its sales by single-digit percentages, Nvidia's top line soared by 94% in its most recent quarter, which ended on Oct. 27.

It's much more tenable for investors to pay a premium for a fast-growing business than it is to pay one for a company such as Apple, which isn't exactly experiencing a surge in sales and profits.