Digital currency bitcoin has risen by more than 200% in 2017, and it actually broke through the $3,000 level for the first time just hours before I wrote this -- and dropped by more than $500 soon after. It's fair to say that not only is bitcoin hitting record highs, but the market is extremely volatile. Many people have made speculative investments in the currency, with no upper limit to the price of a "coin" in sight.

While I never recommend buying or not buying an investment simply because of what a billionaire says, it can be a smart idea to listen to what some of the most successful people in the world have to say. This is why Warren Buffett's investing wisdom is so widely followed, just to name one example. With that in mind, here are what three of the most respected billionaires in the world have said about bitcoin.

Stacks of gold coins.

Image source: Getty Images.

This billionaire sees lots of value, but thinks the price is in a bubble

Billionaire investor and Shark Tank star Mark Cuban seems to have mixed feelings on bitcoin. On the bearish side of things, in a recent series of tweets, Cuban made it clear that he thinks bitcoin is in a bubble.

"I think it's in a bubble. I just don't know when or how much it corrects," tweeted Cuban. He went on to mention that when everyone is bragging about making easy money, it's a sign of a bubble. When I think back to the tech bubble of the late '90s, or especially to the housing bubble of the mid-2000s, this certainly makes sense. "Everyone always thinks that this time is different," Cuban added.

While Cuban was tweeting his comments over a span of about an hour and a half, the price of bitcoin noticeably fell. The billionaire felt that this was further proof of his point, and tweeted a few hours later: "You know it's a bubble when a random twitter thread bounces the price."

On the other hand, Cuban also praised blockchain, the underlying technology behind bitcoin. "I think blockchain is very valuable and will be at the core of most transactions in the future," tweeted Cuban. "Healthcare, finance, etc all will use it."

In a nutshell, Cuban is saying that bitcoin and its blockchain technology does have value. It's just not worth $3,000 at this point in time.

Is bitcoin a mirage?

Warren Buffett is perhaps the most respected investor in the entire world, and hasn't said much about bitcoin recently. However, the Oracle of Omaha notably dismissed bitcoin as an investment in a 2014 CNBC interview.

Buffett essentially said that bitcoin is essentially a more modern version of writing someone a check or sending a money order, and advised investors to avoid it. "Stay away from it. It's a mirage, basically...The idea that it has some huge intrinsic value is a joke in my view."

Not surprisingly, the response by many tech industry heavyweights, such as Marc Andreessen, was to dismiss Buffett's comments, claiming bitcoin is yet another new technology Buffett doesn't understand. And Andreessen may have a point -- Buffett has notoriously avoided investing in new technologies throughout his career, and has actually said it's because he doesn't understand them well enough to invest.

To be fair, remember that Buffett's comments were made over three years ago, and the value of the blockchain technology in particular has been made much clearer since then. So, it's entirely possible that Buffett's viewpoint on bitcoin has changed somewhat. Even so, don't count on Buffett buying bitcoin with Berkshire Hathaway's capital anytime soon.

This billionaire is a fan of blockchain technology

Finally, billionaire entrepreneur Richard Branson is perhaps the biggest fan of bitcoin and blockchain technology of the three men discussed here. In fact, Branson has gone so far as to refer to blockchain as an "economic revolution."

At last year's Virgin Disruptors event in London, Branson specifically mentioned a potential application of using the blockchain to create a better land titling system. He mentioned that in developing countries, land titles are frequently forged or taken from the rightful property owners, and said that a blockchain-based solution could solve this problem once and for all.

Branson has held an annual "Blockchain Summit" on his private island for the past two years, which has resulted in several new ideas and partnerships.

In regards to bitcoin as a currency and whether or not it will work, Branson replied "Well, I think it is working." However, Branson also acknowledged the currency's volatility, and that other similar currencies could emerge that "may be even better."