As a KDE fan, I actually think an amnesic distro like Tails should better go GNOME, because it’s more minimalistic and needs less customizations.

It’s just better for a “run something default, do quick tasks and wipe” kind of scenario.

XFCE is still on X11 so it is not a good choice for a secure private OS. GNOME both secures privileged Wayland protocols and has sandboxing for its thumbnailer, among other important security features. KDE is another option, but is kinda over the top for an amnesic distro.