Honestly, depending on whether you count it or not, LFS. I have not tried Gentoo yet, though I want to one day, for the learning experience, and yet I already know that compiling everything is not something I enjoy.
I can get by with OpenSUSE and Void (kinda), I’ve used Debian for a few weeks, I’ve used Fedora for a month or so, I’ve used Ubuntu for a bit, I’ve tried PopOS for a week or two, I’ve used NixOS for a few months, and I’ve used Arch for most of my time on Linux.
Currently I’m on Arch, but I don’t like rolling releases that much. At the same time, I am also not a fan of immutability, as there are some programs I need that cannot be installed on an immutable distro, so that’s why I’m on Arch. Why am I only using these 2? Because they are the only distros that have all the packages I need (excluding the specialist software that I need for university). By the time I discovered Distrobox (which would solve this problem), I was already on Arch. I’ve also done some changes to my setup and as such, I’ll need to wait for some new features to make their way into program releases and into the NixOS Stable repo with the following release. Until then, I’m on Arch.