For me its KDE.
KDE was the first one I used after getting more comfortable with Linux and leaving Unity behind. KDE was very customizable and extensible, but when you actually started customizing it quickly became unreliable. I stuck with it for a few years then I tried Elementary next and it was pretty polished but it was limited to a specific distribution. After that I went to GNOME and I’ve been using it for 7 years now. It does need a few extensions, but otherwise I’ve found that it works quite well. I think I’ve also changed, I’m not as interested in things like wobbly windows anymore. I just want the desktop environment to stay out of my way, but I also don’t want it to be too bare bones.