EndeavourOS is moving to KDE Plasma for its live environment and offline installer from Xfce. You’ll hear no complaints from me!
I tend to use XFCE on machines with lower specs. It’s a lighter DE. Plasma has always been pretty heavy in comparison, because it’s really customizable and designed to be very good looking, which can be taxing on lower-end hardware.
I think this is outdated advice. Most folks seem to say the memory usage is similar, CPU/GPU usage is a bit higher in Plasma if you leave effects turned on, and disk usage is higher in Plasma.
I primarily care about RAM and my experience with KDE on the Steam Deck is pretty good so it seems like a solid choice.