I was recently studying this question and here is what I found:
- You can use Coinbase if you are in US and you will feel pain because of their fricking commissions
- You can use some exchanges like Bitfinex, Bittrex and some others but still the rate would be awful
- You can use new platforms like Cryptology and some others but there is no information on them atm but there might be the better rate
- You can use LocalBitcoins (which is banned in Russia)

What is your choice?