If you're an investor in digital currencies, there's a good chance you have bragging rights over Wall Street this year. While stocks have historically been the go-to investment for solid long-term wealth creation, it's the nosebleed returns from cryptocurrencies that've stolen the show in 2017.

After beginning the year with an aggregate valuation of just under $17.7 billion, cryptocurrencies now combine to sport a $152 billion valuation, translating to a 760% year-to-date gain. This is the type of gain an in investor might encounter after holding an equity for a decade or longer, not over the course of just nine months and two weeks.

At the center of it all are bitcoin and ethereum, which combine to make up about two-thirds of the aforementioned $152 billion aggregate market cap. The blockchain technology that underlies these digital currencies, along with the option of utilizing these currencies as an alternative payment platform, which has been a major lure for bitcoin, continues to provide reasons for pushing these digital currencies higher.

But what if bitcoin and ethereum investors were overestimating the popularity of digital currencies as a payment facilitator of the future. I mean, sure, the investors in these currencies strongly believe in their future; but what about the rest of the public? A new survey answers that question, and it should concern bitcoin and ethereum investors.

Surprise! Bitcoin and ethereum aren't as popular as you think

According to the recently released survey from Cardtronics and Edelman Intelligence, digital currencies aren't nearly as popular as you'd think. The duo asked Americans what form of payment method they preferred most. The results might surprise you a bit:

• Debit cards (33%).

• Cash (27%).

• Credit cards (22%).

• Digital (15%).

• Check (3%).

Debit cards, not bitcoin, are the most preferred payment method for a third of Americans -- and It's not hard to understand why, either. Getting a debit card is pretty simple -- you usually just need to open a checking account with a bank or credit union -- and making purchases is streamlined since it requires nothing more than a swipe of a card and your personal PIN to make a purchase. Debit cards are also accepted by most merchants domestically. They're not perfect, since there are fewer protections against fraudulent purchases compared to credit cards, but they're the front-runner when it comes to preferred payment methods.

Cash -- yes, that green stuff in your wallet -- remains the second-most popular form of payment. The reason folks still like cash is that it's a tangible form of wealth that'll always be there. Within the survey, 84% of respondents noted worries about data security, and roughly two-thirds said they make payment decisions based on which form is considered to be the most secure. That's up 6% from the previous year, and it's a response to the numerous credit card scandals and hacks we've seen in corporate America over the past couple of years.

Credit cards are also popular with 22% of those surveyed. Of course, we only need to look at aggregate credit card debt to realize how popular they are. Earlier this year, aggregate credit card debt hit $1.027 trillion, a new all-time record that surpassed the pre-Great Recession high. Credit cards offer a number of consumer fraud protections, and quite a few offer cash-back or travel rewards these days. Unfortunately, with interest rates on credit cards higher now, on average, than they've ever been, they can be more trouble than they're worth if you aren't careful.

All the way down in fourth place with 15% of the vote are digital payments. It's worth pointing out that bitcoin and ethereum aren't the only forms of digital payments. Lumped in this category would be mobile transactions utilizing near-field communication chips, or payment networks such as Apple Pay.

Why bitcoin and ethereum could struggle to gain popularity

Though cryptocurrencies like bitcoin and ethereum have made some investors rich, they're probably going to struggle to gain the trust of consumers as a preferred payment option.

To begin with, there just aren't many merchants that accept either currency. I genuinely struggled to find more than a handful of merchants that accepted ethereum using a quick search, with no brand-name companies having stepped up to the plate. Don't get me wrong; a number of brand-name organizations are utilizing a version of ethereum's blockchain in small-scale and pilot projects through the Enterprise Ethereum Alliance, but very few merchants have considered accepting the coins as a form of payment.

Something similar can be said of bitcoin. Even though it does have a handful of brand-name businesses that have accepted its coins since 2014, trying to live off bitcoin would prove incredibly challenging. Unless we see broader merchant acceptance of digital currencies, it's unlikely that the public will come around.

Furthermore, security remains a concern. Even though blockchain technology is touted as being safer, especially given its decentralization, security breaches among cryptocurrency exchanges aren't unheard of. In fact, Mt. Gox, which had been handling around 70% of bitcoin's trading volume before its bankruptcy declaration in 2014, was allegedly the victim of a cyberattack that cost it tens of millions of dollars and 850,000 bitcoin.

Instances like this, and the fact that bitcoin and ethereum aren't tangible forms of currency, give consumers all the more reason to stick with payment platforms they're familiar with. In other words, it'd probably be best to temper your expectations for bitcoin and ethereum.

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Sean Williams has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Apple. The Motley Fool has the following options: long January 2020 $150 calls on Apple and short January 2020 $155 calls on Apple. The Motley Fool has a disclosure policy.