Recently, uBlue. It’s more a family of fedora atomic images but it has taken the pain out of immutability for me. I was using Fedora silver blue and later Sericea a while back, but installing codecs from RPMfusion on it never worked properly and my hw acceleration was always broken. I was on NixOS for a while but had sporadic problems that come with NixOS not using an FHS structure. But uBlue just works. Hardware acceleration works out of the box, and I can easily create custom images with BlueBuild. It’s a very nice ecosystem to create a stable, secure, complete base system. And I run nix on top of it for user packages and home-manager to get all the benefits of both worlds