GDScript for UI and prototyping, c++ for the game logic when its needed or when the game design is stable and we have time to rewrite it. I want to write a GDScript -> C++ transpiler, to be honest.
I wouldnt want to use c# as I dont want the complexity. Our games go on the web, as well, and I don't think c# works there.
Godot 4.0 doesn't support C# on the web and mobile, one of those fabled "Godot $nextver fixes this" things that somehow immediately come up whenever I get hyped up for giving Godot another try.
I think most do use GDScript, but the C# support is very good. If you need great performance in your game scripts, or are familiar with C#, best to start with that.