I will give you a little background on my experience and the app to help paint a better picture of what I need out of the BaaS, and then tell you what choices I have narrowed it down to.
I am a pretty novice programmer, and the entire app will be developed by me. I have developed and released a 2 mobile games, and started work on a Console/PC game using Unity. But I am self taught and have very minimal App coding experience. And I just started with Xamarin a month ago.
The App/Web service would have to have similar functionality of an App/Web service like Eharmony. So it should be both a Mobile App (Android/iOS) and a Website. It should contain user data and then display a "feed" of other users based on certain criteria. So database storage that allows some algorithms to be run on it for sorting. I also would need secure login functionality. I would also need advertizing support. And would prefer to use AdMob, because I have some previous experience.
From my findings I am thinking of going with Azure or Firebase.
AWS seems like it would be to complicated to set up for me to use, and sort of more power than I need or want, right now.
If I disregard compatibility I would want to go with Firebase as it just seems like it would be a better fit for me, and I love the Google ecosystem! If I am able to use Google sheets to do the filtering and what not that would be a big plus cause I have a lot of experience "coding" with Google Sheets. I also like the "live" updating that Firebase has, I don't need it but I would like the option cause I could create a messaging system inside the app/web service
But from what I have been reading the compatibility of Firebase and Xamarin is not very good. I am looking to make this as painless as possible, and I think Azure would be the easiest to implement.
I have heard of a few other BaaS and Kinvey also seemed like a good one, but I am weary because it's a smaller company/community and I don't want it to shut down like Parse.
Sorry for typing so much but I wanted to paint a decent picture of my situation. Thanks!