I can only speak for Silverblue, as I didn’t try other ones yet. But I’m extremely happy with it.
General
I don’t get the difference between rpm-ostree and other techniques, like those from VanillaOS or Aeon, yet. So I can’t tell if ostree is the “best” one
BIGGEST pro (in my opinion): the rebase-function (see the following)
Working with it feels very “clean”, as your base-OS doesn’t get crammed with trash programs
You containerize pretty much everything if you can. Flatpak and Distrobox are your friend.
Should be more reliable, since there’s “your” stuff and “the OS’ stuff”, and every system is the same -> devs can fix bugs better
“Official” (vanilla) Silverblue
The oldest one around. Big developer- and userbase
Very robust and stable
But also minimalist (no additional packages preinstalled)
Comes only with Gnome or KDE
You need to layer/ install essential packages yourself, which somehow isn’t the recommended way to install stuff. I yet still have to find out what disadvantages this has.
Universal-Blue (uBlue)
Isn’t a distro/ fork of SB, but takes advantage of the rebase feature.
Basically, you can choose from where your distro draws it’s OS-base. So, it’s just a repository for OS-images.
Comes with essential packages and tweaks OOTB (distrobox, 3rd party stuff, Nvidia drivers, etc.), which aren’t layered, but part of the image
Everyone can publish their image. There’s the “normal” SB with QOL-stuff added, there are some DE-spins (e.g. XFCE), some are similar to SteamOS, and so on.
CON: I don’t know how reliable and “bloated” they are compared to Vanilla SB.
I can only speak for Silverblue, as I didn’t try other ones yet. But I’m extremely happy with it.
General
“Official” (vanilla) Silverblue
Universal-Blue (uBlue)