I've got a co-worker who's quite impressed with Firebase. https://www.firebase.com/

Also, I saw a really cool presentation on the Azure platform. It supports push notifications, and even has a multiplatform template generator. https://azure.microsoft.com/en-us/services/app-service/mobil...

Both platforms feature a database and authentication.

The one that you know best, in which you are the most productive. It's all just Web Services at that point. Nothing special about it being in support of a mobile app.

What I do is not look for the "best", but keep scaling 10x. So start with targeting 1,000 users, then 10,000, then 100,000 and so on.

Parse is awesome to start with at that 10,000 user mark. Parse seems to scale its costs poorly though.

Past the smaller scale you have a lot of choices. Azure. AWS. Firebase. IBM's thing. All have their pros and cons.

What features do you need?

You might want to look at this:

http://www.kinvey.com/blog/3652/the-evolving-enterprise-back...

(the infographic on the blog)

If you need to spin-up notifications support quickly, Parse is pretty good. You can roll your own, but Parse is free until you get big.