I have tried Parse Server which I like in general except for the part that it misses push delivery.
Same with Firebase. It seems to be very stable and has good speed. Lacks the push delivery.
CloudKit is good but my game will demand much logics and I will have to write much custom code for this on the server side.
Amazons options are not that interesting to me.
I am considering making my custom server scripts for the whole game, for control and speed.
But I wonder which of all those services are the most optimal regarding to velocity?