So I think Guix (and Nix) is the most technologically advanced package manager in existence, and I hope someday all package managers work like Guix.
One other very interesting feature about Guix (which I don’t think Nix is doing yet) (which Nix also does) is that they have implemented a fully verifiable bootstrap, meaning every step of building the kernel, including the steps taken to build the C compiler toolchain, are produced by code that is simple enough for a group of humans to check for correctness and safety. Also, every step of the build process exists in the package repository, with no reliance on externally built binaries for anything, not even the C compiler toolchain. They accomplish this with a multi-phase bootstrap process, where a smaller, simpler C compiler is used to build GCC.
Do I use Guix? Well, no. Simply put, it is not quite to the point where it just works on a lot of the computer hardware that I own. With a bit more work, with a few more developers, and a bit more money invested, Guix could pretty soon become as reliable and useful as Debian or Fedora. But it is not quite there yet. And frankly, I have other more important things to do than worry about debugging problems with the operating system I am using.
I would go with Guile, because it is built-in to the Guix Package Manager which is a really good general-purpose package manager.
It ticks several of your boxes:
It also has pretty good libraries for system maintenance and reporting: