Debian Slim all the way. musl is only good when you are building for and testing against musl. Third party software on musl has burnt me enough times to know that sticking to glibc is the way to go unless you like that sort of pain.
Footnote: I actually love musl, just for my own software that explicitly targets it and is validated against it.
Footnote: I actually love musl, just for my own software that explicitly targets it and is validated against it.