Bazzite and HoloISO are immutable, that's a huge difference (good or bad, depending on your use case), and If you don't care about VRR & HDR, Bazzite also supports GNOME the other two distros don't.
Also, out of the three, as far as I know, Bazzite is the only one that supports Nvidia.
I also need to evaluate which distros have the native Steam packageor if they use the Steam flatpak, since the Flatpak version doesn't support libraries on multiple drives. That would also be a huge difference.
That's the main difference between Holo and Chimera. Their upstream setups with SteamOS are essentially the same.
Also, Nvidia drivers don't work with any of the extra Valve tools in SteamOS (gamescope), so if you're going the Nvidia route, I wouldn't recommend using anything based on SteamOS anyway.
I have been using Bazzite for about 3 months now, it has worked quite well for me on my two desktop systems.
I can not use the SteamOs mode on my Nvidia system, but it still works decently well as a normal desktop running steam.
my AMD desktop system does use the SteamOs look mode.
I was using Holoiso last year, but had numerous issues, so gave up on it. The other similar distros, I recall testing, and not lasting a day with them for various reasons.
So for now Bazzite is my go to.
Side note: just noticed on reddit the /r/Bazzite sub is now banned for being unmoderated.
Not that there was a lot of traffic there anyway, but that is a major issue with Bazzite, it's a bit fringe, and while a lot of silverblue stuff does apply, it's still a small community it seems.
I tried all of them and none can handle adding custom kernel modules properly. The longest I spent was on Bazzite, because I could build my custom rpm for akmods, but then it has issues sometimes that the image was built with newer kernel than available and it fails due to being unable to install kernel modules. Long story short it requires full image build. The viable solution would be to ask devs to include the driver I need in their akmods collection, but that’s some random github fork of old driver removed from mainline kernel long time ago. I’d much rather have ability to add that myself.
I tried Nobara and used its gamescope-session package. It’s just as complete as Bazzite and the final touches are far easier to get. It’s still traditional Fedora, but gaming and HTPC ready almost out of the box.