As someone who uses both for different personal projects:

- I use zig as my build system for both rust, zig, C libraries and linking since the build system works really well for this purpose

- When I need to write applications or libraries that can benefit from compile-time code, I always try and use zigs since it's much easier to use comptime then a combination of rust macros and generics

- I like the zig async story a lot better. Or at least it's much easier to wrap my head around and write code in compared to rust + tokyo

On the other hand, sometimes I know a project will benefit from the borrow checker or I want to use some of the awesome rust crates that the community made and I'll use rust instead.