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.