I use Openbox right now. Sleek and minimal.

I used i3 and Sway for a long time, but enough applications don't play nice with tiling (i.e. they design for stacking windows) that it's a hassle.

XFCE is pretty slick. Only nitpick I had was I couldn't get apps to start on a given desktop at startup, IIRC.

It's been too long since I used KDE or Gnome so I can't speak to those.