The companies that gain most directly are the ones that build the required GPU and ASIC mining rigs.
How Bitcoin Mining Works
New Bitcoins enter into circulation whenever new transactions are confirmed into the networked blockchain ledger. This involves using expensive computational hardware to solve repetitive — and pointless — math problems.
This intensive computational process gives the appearance of creating value, but all it really does is increase the sale of GPU and ASIC mining rigs; and convert a lot of electricity into heat.
Investment or Speculation?
Cryptocurrencies can indeed reduce the government monopoly on money, and force governments to be more fiscally responsible.
But while it's astute to transact in cryptocurrencies, investments should still be backed by tangible assets. Cryptocurrencies have no tangible underlying assets, and thus trading in them is speculative by definition.
True investments such as Real Estate and Value Stocks generate income. They also have tangible assets backing them, and are therefore intrinsically hedged against inflation. When a currency gets devalued, the price of a tangible asset automatically increases.
Cryptocurrencies do not have any of these benefits. In short, cryptocurrencies are great for transacting; but not for investment.
Currency or Trading Card?
Since Bitcoin provides high liquidity without generating revenue on its own, it comes closer to being a currency than an investment. But a true currency such as gold is naturally limited, and has some real-world utility. Bitcoin satisfies neither requirement.
“Money is gold, and nothing else.”
J. P. Morgan, Testimony Before the House of Representatives (1912).
Perhaps the closest analogy for Bitcoin is therefore that of a publicly-owned Trading Card, limited by mutual agreement and of no real-world utility; but having collectible value.
Bitcoin is therefore perhaps the world's first crowdsourced electronic Fiat Currency.
Buffett on Bitcoin
As Buffett says, an investment is something you should be OK to hold on to if the market for it were to close for 10 years. Cryptocurrencies do not generate any income, and have no tangible asset value.