What database to choose from? : <p>Realm Database or MySQL or MongoDB or the standard Firebase. </p>

<p>I am curious why would anyone choose one over another. I am in a group project and one of the members in the group suggested that we should use Realm Database over Firebase. He tried to explain to me the reason but I was not able to comprehend. </p>

<p>What has your experience been like? Is one database more user-friendly over another? 
Firebase seems to have very nice documentation. </p>

<p>Which one would you guys suggest?</p>
