Are you looking for a new fintech name to add to your portfolio? It's certainly an area worth a look. The convergence of these two distinct sectors (finance and technology) is creating some incredible growth opportunities.

In fact, it has arguably made for too many options. Take Nu Holdings (NU -0.29%) and SoFi Technologies (SOFI -3.74%). Both are great online banks, leading their respective markets. But some investors may only have room for one or the other. The question is, which one?

Comparing and contracting Nu Holdings with SoFi Technologies

You've likely heard of SoFi. A company launched in 2011 as a platform to help college graduates manage their student loans has since become much more. It's truly a full-blown chartered bank with all the expected offerings -- checking accounts, lending of all types, credit cards, investment services, and even insurance. As of the end of September, it was serving nearly 9.4 million customers, extending a four-year growth streak of uninterrupted quarterly customer growth. Its annual revenue on the order of $2.5 billion produces yearly net income in the ballpark of $200 million. That's fantastic for a young bank without any physical branches. Yes, SoFi is truly a 100% online-only banking option.

Nu Holdings is a similar company but with a few important differences. Its Nubank business serves more than 110 million customers, for instance, and is on pace to turn roughly $4 billion worth of revenue into income of $2 billion despite offering fewer services; clearly, those it does have are higher-margin offerings.

So why have you heard so little about Nu (presuming you've heard of it at all)? Because it doesn't operate in the United States. It only operates in Brazil, Mexico, and Columbia, where the online banking business itself is quickly growing, and where competition isn't quite as robust ... at least, not yet. It's coming, though. Market research outfit Technavio believes that the banking-as-a-service industry -- aka, online banking -- is poised to grow in Latin America at an annualized pace of 19.5% through 2028.

As a market leader, Nu is well positioned to capture at least its fair share of this growth.

And the winner is...

It's a tough decision to make between these two fintech names.

Nu Holdings clearly enjoys better growth prospects by virtue of its bigger addressable and largely underserved market. Latin America is home to 665 million people. However, each Latin American country regulates banking businesses differently, which will add to the complexity as Nu expands its footprint. There's also no denying that several South American countries are experiencing political unrest, which adds to the uncertainty of Nu's foreseeable future.

On the other hand, SoFi's growth prospects might not be quite as compelling, but at least it has a somewhat predictable growth path that's easy to keep tabs on from where you (probably) sit. So, if you can only invest in one of these names, SoFi Technologies would probably be the better bet for most investors.

That said, if you already have a stake in Nu Holdings, you're hardly doomed. The stock just comes with greater risks to match its potential higher rewards. The online bank's actual growth potential is a bit clouded due to South America's backdrop of uncertainty. That's in contrast with SoFi's future -- it might feature slower growth, but it should also be more predictable, and enjoy a much longer growth runway.

The numbers: SoFi's 9.4 million U.S. customers are only a fraction of the country's population of 336 million, the majority of which have or will need banking services of some sort. As a greater share of the adult population becomes digitally native -- in other words, people who have only known a world in which using computers and mobile phones is the norm -- online banking will become more popular while brick-and-mortar banking will become decreasingly important. A recent report from Straits Research forecast that North America's digital banking market will grow at an average yearly pace of 12.7% through 2032. Domestic investors will be able to closely follow SoFi's progress in capitalizing on this opportunity.

And it's off to a great start. Analysts expect this year's top-line growth of more than 24% to be followed by revenue growth of 17% in 2025. While its percentage growth rates will likely continue to slow down, its absolute whole-dollar growth may not even start showing signs of decelerating until the 2030s.

Different enough

If you've just got your heart set on investing in Nu Holdings, that's OK. Again, its shareholders are far from being on a collision course with disaster.

Do take a step back and consider how Nu Holdings fits into your portfolio's bigger picture, though. It's seemingly more of a growth stock that happens to be in fintech. You can find similar growth potential in a variety of sectors and industries. That's in contrast with SoFi Technologies, which is arguably more of a focused fintech stock that happens to be in a fast-growing sliver of the financial sector. There are fewer ways to expose your portfolio to that particular industry with this particular risk-versus-reward scenario.

Of course, although you don't want to own more stocks than you can effectively manage and monitor, there's a case to be made for owning both Nu and SoFi since both are compelling. You might just want to scale back each position from your normal stake size if that's the route you want to go.