If I am using KDE, should I be using Plasma, Plasma Wayland, or Full Plasma Wayland… on a reasonable PC?
And why?
And is this too difficult to answer? 
Try them all out, and see.
I’m still using plasma (X11). I occasionally try Wayland, but it still seems not quite ready.
You should evaluate the options for yourself, as your experience may not reflect others. Some of this is hardware related, and some down to your particular desktop requirements. Like Neil, I’ve tried all the options, and while I find the Wayland environment works ok within VM guest environments, this may not be the case in a bare metal environment (especially with respect to certain graphics cards). I’m still principally using plasma (X11) for day to day use. That will change within a few years I suspect.
These might of interest to you…
https://www.debugpoint.com/2020/07/kde-plasma-5-20-wayland/
https://linuxreviews.org/KDE_Plasma_Will_Default_To_Using_The_Wayland_Display_Server_On_Fedora_34
https://www.phoronix.com/scan.php?page=news_item&px=More-Plasma-5.20-Wayland-Fixes
Well, there you go…
Should have actually tried to login using the other options, before I posted here…
Just tried both:
- Wayland: Black screen, mouse pointer that changed size when over the panel (but couldn’t see the panel…), also must have been windows open on the black screen, as moving mouse pointer around the screen, changed the pointer to resize, etc.
Killed session (using Ctrl-Alt-Backspace), then logged back in using:
- Full Wayland: Same result, except when trying to get back to the login screen, it locked up…
Back to straight Plasma for me!!