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?
I also use kraken since its very friendly user and also I use Codex though this one is a new exchange but known to be supportive and prestige in regards to their service and customers
But there are also other popular exchangers that legit and tried and tested but the fees are higher specially for newbies