GrapheneOS has an incredibly easy installation as it's entirely done through your browser (though it doesn't work on Firefox unfortunately).
As for Sandboxed Google Play versus MicroG, I believe app compatibility is much better. It's not perfect as I've come across multiple apps that simply don't work on Graphene but I hear the situation is a lot worse with MicroG. There have also been quite a few instances in the past of MicroG leaking data it shouldn't be.
I started with Arch and loved it but just recently switched to openSUSE and it might be even better.