It's tough to pick out competitors against Firebase as I'm really unsure and doubt there's another product exactly like it. As mentioned before Firebase literally does everything you can imagine for a mobile application but doesn't get insanely deep in one feature or action. It involves analytics, notifications, database, cloud storage, CRM, attribution, deep linking, dynamic linking, crash reporting, and so much more. It's not amazing at any specific thing (except maybe their database which is AWESOME) but good at all of it.
We used Firebase for everything in the beginning as it was free and got the job done then as we grew, we started to pay for and integrate with more advanced systems but will always have Firebase in there as well.