There are hundreds of Bitcoin exchanges which anyone can sign up for and start buying Bitcoin quickly and effectively. Personally, I use Gemini or Kraken. Gemini has an excellent interface and low fees, while Kraken offers some of the best crypto assets and is one of the oldest exchanges in existence.
The real question is... What is your favorite Bitcoin exchange?
One of my favorite exchange on which I most often to used was Kucoin and IDAX, because its proven and tested to me that I earned moderately and sometimes huge profit anyhow, and I never encounter any such problem issues too.