What is the best Google Play Store alternative?

Despite the Google Play Store coming pre-installed on most Android devices as a one stop shop there are actually many alternatives to what Google offers. Ranging from completely open source stores like F-Droid to flat out competitors to Google with the Amazon Appstore there are actually quite a few alternatives. Some may not offer as much ease of use, while others may offer more, but in the end competition is a good thing that pushes each and everyone to better themselves. The trouble is, who knows which one is worth the time to invest in? This specific question, filled in by the users who use these stores should offer some insight as to what each one offers, making it easier to know which one is right for you.