Back End for AngularJS App – Firebase, MongoDB, PGsql? Etc Etc.

Was thinking for an app that works on both mobile and web, Firebase is ideal for its REST Api and real time sync. Also Angularfire makes it easy to hook all of the components up. However, I have also seen a couple of apps using MEAN stack with MongoDB. Whats the main differences that one should know between these 2 stacks?

What I understand is Firebase has less control but needs less codes and has less quirky errors. But that also means the data is not query-able or not as easily manipulated and search engines are not optimised to track Firebase stuff.

Would like to hear your experiences on the various backend solutions used (not exhaustive). Feel free to talk about the requirements from your project that needs various stacks.

Some other considerations I have: - scalability - costs (user number/ usage level vs. costs)- both are free until usage hits a certain level - code maintainability - code portability - device compatibility