> Gentoo is probably in-between these two, although I believe Gentoo is a more opinionated distribution than Arch regarding how the system is structured (see custom init, custom udev etc).
Gentoo offers even more freedom of customization than Arch. Choose your init system, your udev variant, your main Python version, set around 100 build time options for ffmpeg and so on.
LFS is great for learning and looking under the hood, but for a system that you actually use daily, Gentoo has no rival.
If customization is a goal I'd look into Nix(OS) as well. Source distro with binary caches for the default build options. Oh, and your setup becomes trivial to reproduce (just copy the config files). Oh, and you can easily revert your machine to a previously known working state if you screw something up.
Gentoo offers even more freedom of customization than Arch. Choose your init system, your udev variant, your main Python version, set around 100 build time options for ffmpeg and so on.
LFS is great for learning and looking under the hood, but for a system that you actually use daily, Gentoo has no rival.