What we as investors witnessed from cryptocurrencies last year is something that may not be duplicated again. A single asset class gained more than 3,300% in market cap (almost $600 billion) over a span of just 12 months. It's essentially a lifetime's worth of gains for some investors that were crammed into only one year.

Of course, 2018 hasn't had nearly the same flair as 2017. After beginning January on a high note, cryptocurrencies fell off a cliff, losing 67% of their market cap, from peak to trough, between Jan. 7 and Feb. 6. Everything from the prospect of increased regulations in South Korea to Facebook banning cryptocurrency advertisements hit the market hard.

Then again, some aggressive investors saw the drop as a buying opportunity. In the two weeks following Feb. 6, digital currency valuations again doubled. This whipsaw action has become commonplace for a market that's predominantly driven by emotionally charged retail investors.

Take note: These virtual currencies could still double

Yet even with a plethora of risks and the volatility, a handful of virtual currencies continue to stand out thanks to their proprietary blockchain technology -- the digital, distributed, and decentralized ledger that's responsible for logging all transactions. While guessing the next move in virtual currencies has proved to be more of a crapshoot than Wall Street typically prefers, the following three cryptocurrencies may have a genuine shot at doubling from their current market caps.

1. Ethereum

Feel free to call me nuts, but I believe the second-largest cryptocurrency by market cap has the potential to double and/or surpass bitcoin in total value. In fact, I've been of the opinion for quite some time that Ethereum deserves to be the most valuable cryptocurrency in the world, by market cap.

Ethereum's selling points are its blockchain and enterprise clients. Its blockchain has three very distinct differences from bitcoin that should allow it to close the market-cap gap with the world's largest cryptocurrency. First, Ethereum can process almost three times as many transactions per second as bitcoin can. Not only are these transactions processed more quickly, but they're considerably cheaper, with the average transaction on the Ethereum network costing less than $1, and the average bitcoin transaction cost pushing north of $28.

Secondly, Ethereum's blockchain transcends currency-only applications. It not only has the potential to transform how financial institutions transmit money, but it can be pivotal in helping monitor supply chains, creating digital identifications, and logging medical records, to name a few ideas. Not surprisingly, 200 organizations from around the globe are currently testing a version of Ethereum's blockchain, via the Enterprise Ethereum Alliance, from a multitude of different sectors.

Third, Ethereum's smart contract protocols are a game changer. Smart contracts aid in the verification, facilitation, and enforcement of a contract. In other words, they're the rules that make digital contracts binding, at least relative to murkier paper contracts. Smart contracts can be also be molded to fit the needs of a business, making them perfect for a host of industries and sectors.

While bitcoin struggles with slow processing times, high transaction fees, and is stuck with currency-only applications, Ethereum's network is scratching the tip of the iceberg.

2. Nano

If you want a true cryptocurrency wildcard, it would be Nano (formerly known as RaiBlocks). Nano brings an extremely unique blockchain design into the mix, as well as some groundbreaking processing speeds that could turn heads.

Rather than relying on a single central blockchain, which with an open-source network often means needing to reach a massive amount of people to achieve consensus anytime something big is about to happen with the network (e.g., a software or hardware upgrade), Nano sports a block-lattice blockchain. In other words, each user has their very own blockchain that they can control, meaning there's no large consensus that needs to be reached... ever. Because each account has its own blockchain, the network should, in theory, be rapidly scalable without impacting performance.

How fast is the Nano network, you ask? According to the horse's mouth, Nano is capable of processing an incredible 7,000 transactions per second, albeit hardware upgrades in the near to intermediate future are expected to push this figure even higher. Relatively speaking, Visa can process in the neighborhood of 24,000 transactions per second, meaning Nano is closer than any other cryptocurrency at present to the payment processing kingpin. By comparison, bitcoin maxes out at a mere seven transactions per second.

It is worth pointing out that because of the setup of Nano's blockchain, it requires a peer-to-peer payment to be broken down into two separate transactions: one where the sender removes money from their account, and another where the receiver adds the funds to his or her account. It may sound cumbersome, but it's lightning-fast and, perhaps best of all, free.

The downside? Nano doesn't have any major partners as of yet. However, with these processing speeds, it's just a matter of time.

3. Qtum

A final virtual currency with the potential to double in value from its current levels is Qtum. Qtum's blockchain was developed with the idea of taking the best aspects of bitcoin's infrastructure and Ethereum's Virtual Machine, then tweaking it with proprietary additions. This created a blockchain that incorporates smart contract protocols and, despite future updates, will remain compatible with bitcoin gateways and existing Ethereum smart contracts.

In January, the Qtum Foundation noted that it would be announcing five major partnerships in 2018. Two of those partnerships were announced in January, just a day apart. The first involved 360 Finance, a subsidiary of Qihoo 360, a Chinese cybersecurity company that was taken private in 2016. Qihoo 360 is also the parent behind 360 Browser and the 360 Search engine in China, which currently ranks third in search market share. This partnership with 360 Finance creates a blockchain laboratory where, along with BTN Foundation, all three will put their heads together to develop cutting-edge blockchain solutions.

The very next day, Qtum announced that it was partnering with Baofeng Bokocloud to achieve the world's first blockchain consensus network service. Baofeng's media player is a video and streaming service in China with more than 200 million users, and it's believed the company will use Qtum's blockchain for payments made to the company, as well as copyright protections.

What's far more exciting is what Baofeng is doing for Qtum's blockchain. Utilizing its Bokocloud service, Baofeng plans to increase Qtum's network to over 50,000 full nodes, pushing it well beyond the scalable potential of bitcoin, and even Ethereum. Under the right conditions, Qtum could flourish.