Best Practice to implement Cloud Load / Save for a mobile game

Hello,
Im investigating the best practice to save player data (locally and on the cloud). For our previous mobile game, in 2014, we used Cloud Once with a proprietary serializer (any JSON library I tested was way too slow) but our serializer is lacking version tolerance and this has become a serious problem.
Nowadays which are the best practices to implement Cloud Load / Save for a mobile game? Is there any trustable asset that automate this process other than Cloud Once?
A collaborator suggested Google Firebase (https://firebase.google.com/products/realtime-database), which is cross platform so players can import progression from Android to iOS and viceversa but you have to implement a custom player identification or use fabeook ID. Not sure the average user trust an indie app enough to give his facebook ID anyway.
Any suggestions?

 

Just found that there is authentication tool in Firebase:
https://firebase.google.com/products/auth/

 

So what do you think about using Firebase database and authentication instead of Google and Apple services?

 

JSON is the answer you rejected. That's what I use.

 

Im not talking about the data format but the best practice to save game data to cloud / external server.
Is there anybody that is using firebase to save game data to cloud?

 

Ah. Can't speak to that personally, and I wouldn't be surprised if the answer was "nobody."

 

Asking what is the "best" requires anyone who can answer you to have already tried and thoroughly evaluated all possible options in a project similar to yours. The number of people on this forum who have done that already is likely 0.