I use LXDE on my new boxes, but on a 15 year old machine I wasn't sure what the Linux distro had defaulted to. I was surprised to see it was KDE. That machine takes 30 sec to decrypt the disk encryption key (stupid proof of work functions!), but the desktop environment is as snappy as LXDE on high-end 2026 machines.

I haven't compared those two with XFCE recently, but they all seem fine these days.