Kraken works well through SEPA, has an easy verification process (expect 4-6 weeks vetting with current backlog) compared to Bitstamp, and is very knowledgeable when it come to cryptography and security. As of early 2017, this platform has been re-positioning themselves as a crypto exchange by adding multiple new altcoins. I've written an in-depth Kraken review with everything you need to know..
Luckily, the spread between the bid and the ask price is very low, most of the time ranging between 1 and 2 dollars. At a current bitcoin rate of $819, this amounts to an added cost of 0.1 to 0.25%. You only pay the spread if you want to enter a trade right away with a market order. If you placed a limit order to buy and you’re willing to wait until someone wants to sell, you can purchase your bitcoins at a small discount at the bid and later sell them at the ask, pocketing the spread in the process.

The legal status of cryptocurrencies varies substantially from country to country and is still undefined or changing in many of them. While some countries have explicitly allowed their use and trade,[51] others have banned or restricted it. According to the Library of Congress, an "absolute ban" on trading or using cryptocurrencies applies in eight countries: Algeria, Bolivia, Egypt, Iraq, Morocco, Nepal, Pakistan, and the United Arab Emirates. An "implicit ban" applies in another 15 countries, which include Bahrain, Bangladesh, China, Colombia, the Dominican Republic, Indonesia, Iran, Kuwait, Lesotho, Lithuania, Macau, Oman, Qatar, Saudi Arabia and Taiwan.[52] In the United States and Canada, state and provincial securities regulators, coordinated through the North American Securities Administrators Association, are investigating "bitcoin scams" and ICOs in 40 jurisdictions.[53]
Ethereum is an open-sourced, public blockchain-based platform that enables the development of decentralized applications along with smart contracts. Ethereum focuses on running the code of these applications rather than being a peer to peer electronic cash system like many other cryptocurrencies. The project enjoys enormous community support and boasts the most significant active developer community in the cryptocurrency space. Scalability on the network is an issue, but there are many projects underway to address these issues.

There are many ways you can plug into the Ethereum network, one of the easiest ways is to use its native Mist browser. Mist provides a user-friendly interface & digital wallet for users to trade & store Ether as well as write, manage, deploy and use smart contracts. Like web browsers give access and help people navigate the internet, Mist provides a portal into the world of decentralized blockchain applications.

What separated these survivors from the quitters and the double-downers, Carlson concluded, was simply the price of electricity. Survivors either lived in or had moved to places like China or Iceland or Venezuela, where electricity was cheap enough for bitcoin to be profitable. Carlson knew that if he could find a place where the power wasn’t just cheap, but really cheap, he’d be able to mine bitcoin both profitably and on an industrial scale.
The utilities’ larger challenge comes from the legitimate commercial operators, whose appetite for megawatts has upended a decades-old model of publicly owned power. The combined output of the basin’s five dams averages around 3,000 megawatts, or enough for the population of Los Angeles. Until fairly recently, perhaps 80 percent of this massive output was exported via contracts that were hugely advantageous for locals. Cryptocurrency mining has been changing all that, to a degree that is only now becoming clear. By the end of 2018, Carlson reckons the basin will have a total of 300 megawatts of mining capacity. But that is nothing compared to what some hope to see in the basin. Over the past 12 months or so, the three public utilities reportedly have received applications and inquiries for future power contracts that, were they all to be approved, could approach 2,000 megawatts—enough to consume two-thirds of the basin’s power output.
Transactions that occur through the use and exchange of these altcoins are independent from formal banking systems, and therefore can make tax evasion simpler for individuals. Since charting taxable income is based upon what a recipient reports to the revenue service, it becomes extremely difficult to account for transactions made using existing cryptocurrencies, a mode of exchange that is complex and difficult to track.[66]

I won't delve too deeply into the history of Bitcoin or its hordes of both unique and flash-in-the-pan spinoffs, but I do want to point out that you can't actually mine Bitcoin with regular computers anymore. It requires specialized and expensive hardware called ASICs. However, you can mine other coins and convert them to Bitcoin through a variety of exchanges and services. You can also earn Bitcoin by "lending" your computer's processing power to services like NiceHash which pay out in Bitcoin. But that's another rabbit hole for another time!
Coinbase does not charge to transfer bitcoin from one user to the other, which is the point of blockchain. But if you want to transfer money to or from an outside exchange, such as a US bank account, Coinbase charges a small conversion fee. The charge is 1.49% with a $0.15 minimum if you are using a bank account and 3.99% if you are using a credit/debit card. I’d try to avoid funding with a credit card unless you get ample reward points to offset the higher fees.
Cryptography is an art, not a science. And the state of the art can advance over time. Advances in code cracking, or technical advances such as the development of quantum computers, could present risks to cryptocurrencies and the Ethereum Platform, which could result in the theft or loss of ETH. To the extent possible, Stiftung Ethereum intends to update the protocol underlying the Ethereum Platform to account for any advances in cryptography and to incorporate additional security measures, but it cannot predict the future of cryptography or guarantee that any security updates will be made in a timely or successful manner.