Historically speaking, the stock market has been the greatest creator of wealth. Sure, it hits its rough patches from time to time, with 20 bear markets in the S&P 500 occurring over the last 90 years, according to data from Yardeni Research. But at the end of the day, stocks have returned an average of 7% annually, inclusive of dividend reinvestment, and when adjusted for inflation. Compared to bonds, commodities, CDs, and other assets, the stock market has trounced them all over the long run.

Of course, last year's cryptocurrency craze ran circles around traditional equities, including stocks. After beginning the year with a combined market cap of just $17.7 billion, the aggregate market cap of all virtual currencies by year's end had surged to $613 billion, equaling a climb of more than 3,300%. There may not be another year like this for any asset class for as long as we live.

The stock market, however, holds one key advantage over the cryptocurrency market: diversification.

Diversifying just doesn't work with cryptocurrencies

Generally speaking, diversification -- the ability for investors to buy stocks in different industries and sectors, or based on market cap, growth rate, or dividend yield -- has allowed investors the opportunity to maximize their long-term capital appreciation potential. If one sector is doing poorly, a diversified portfolio might be hedged with another industry or sector that's thriving. Plus, with the ability to load a diversified portfolio with dividend-paying stocks, complete with reinvestment, it's often easy to build wealth over time. All it really takes is patience, discipline, and the resolve to buy stocks at regular intervals over time, regardless of how "high" or "low" the market is trading.

With cryptocurrencies, diversification simply doesn't exist. We'd like to think it does, as there are more than 1,600 investable virtual currencies, each with their own plan of action and often proprietary blockchain -- the underlying digital and decentralized ledger responsible for recording all transactions without the need for a bank. But the fact of the matter is that most cryptocurrencies tend to move in tandem with bitcoin, the largest digital currency of them all. This association almost always negates the impact of diversification.

Why diversification fails in the virtual currency realm

You might be wondering why buying a bunch of different virtual tokens doesn't help offset some or all of your losses as it does when buying stocks. I believe the answer is fourfold.

First, there's a clear lack of differentiation. There are, as noted, over 1,600 investable cryptocurrencies for folks to choose from. That's simply too many. You could probably get rid of 1,500 of them, and virtual currency investors would still struggle to keep track of the partnerships, projects, and missions of each of the remaining digital currencies. It's just impossible to weed out which virtual currencies have staying potential and which don't.

Second, there are no fundamental metrics for investors to examine, making a comparison between virtual currencies both difficult and arbitrary. At best, investors can look to project partnerships and processing speed as a few noteworthy comparisons, but that should be hardly enough to decipher whether one cryptocurrency will outperform another over the long run.

Third, there's the disassociation between blockchain technology and the actual tokens themselves. The issue with nearly all cryptocurrencies is that their potential value is tied up in their blockchain and its ability to benefit an industry or sector. Investors who buy into virtual tokens rarely, if ever, gain ownership in the blockchain those coins are used on. Without ownership in the asset that matters, it leaves investors to more or less go along for the ride.

And finally, let's not forget that crypto trading is primarily comprised of short-minded retail investors. These often emotional investors don't have the wherewithal to stick around for the long term, meaning any news event could send them running for the hills. We've witnessed more than one scare with bitcoin and other large digital currencies that sent the entire crypto market tumbling, with basically no exceptions.

What's the smartest way to play the crypto market?

You might be wondering: Is there a good way to get in on the cryptocurrency craze without risking the roller-coaster ride that's become endemic in practically all virtual tokens? I'd tentatively say yes, but only if you're willing to buy into stocks that hedge their bets on more than just virtual currencies.

I'd suggest the safest way to play the cryptocurrency market is through the graphic processing unit (GPU) manufacturers, NVIDIA (NASDAQ:NVDA) and Advanced Micro Devices (NASDAQ:AMD). Both NVIDIA and Advanced Micro make GPUs that cryptocurrency miners use to validate transactions. Being the first to solve these complex mathematical equations, which are a product of encryption within a blockchain, entitles crypto miners to a block reward that's paid out in tokens of the virtual currency being mined. Though the margins on cryptocurrency mining have come down significantly from where they were in December 2017, it's still quite profitable for miners to validate transactions and collect their reward. This puts NVIDIA's and AMD's GPUs in high demand.

The advantage of buying one or both of these companies as a cryptocurrency play is that they have a lot else going on beyond just GPU's being sold to miners. Enterprise customers and the gaming industry still make up the bulk of sales for these giants, allowing crypto-based GPU sales to be the icing on the cake.

Nevertheless, NVIDIA and AMD aren't absolved from downside, either. In fact, you could say the two are stuck in a pervasive cryptocurrency conundrum. As a result of the high demand for GPUs, graphics card prices have shot through the roof. In doing so, it's angered their core gaming customers, who are being forced to pay significant premiums for graphics cards at the moment. These companies could risk alienating their core customer and do nothing or they could create a GPU specific for miners, hurting the growth they've received from miners by increasing supply.

While that's not exactly great news, I still believe NVIDIA and AMD are the best way for investors to gain exposure to cryptocurrencies without suffering through the wild moves associated with buying actual virtual tokens.