I've played around with NixOS, Silverblue, and MicroOS (has recently been renamed Aeon) in VMs and really dig the concept. My general thoughts are:

NixOS - a genius idea but quite a steep learning curve as you have to throw out a lot of what you know about traditional Linux OSs and learn to do things the Nix way. Is too much for me to use as a daily driver, personally, but for people who need to spin up reproduceable systems super quickly, it would be amazing.

Silverblue - much more user friendly than Nix, but (like Fedora) the out of the box experience is a little awkward, especially if using vanilla Gnome with no extensions or modifications doesn't appeal to you. If not, then you're going to have to layer on things like Gnome Tweaks and Extension Manager and that can be a little confusing if all you're used to doing is running dnf install package in a terminal.

MicroOS / Aeon - This is, IMO, the best of the three for beginners because it comes with a lot of quality-of-life additions out of the box: distrobox, Gnome Tweaks, and Extension Manager are already built-in so you don't have to figure anything out (well, apart from how to use distrobox of you aren't already familiar). The only thing I think that Silverblue does better than Aeon is updates, which are a little opaque in the latter. Also, because Aeon is based on OpenSUSE Tumbleweed it is, in theory, less of a stable base than Fedora. (edit: oh, and documentation too! Silverblue is much better in that regard.)

I haven't tried Vanilla OS yet, but it looks pretty interesting. I'm waiting for the 2.0 Orchid release where they'll be moving to Debian Sid before I take it for a test run.