Currently KDE. I love how customizable it is. For the most part, I've found I can get it to work exactly how I want, without having to do any weird dconf editing or recompiling. I also like that it's Qt-based because a lot of my apps use Qt so that provides a fairly consistent look and feel.

I used to like GNOME, but I started getting really tired of how restrictive it can be (e.g. aforementioned dconf editing). It seems like the GNOME team have copied Apple's "we don't think you need to be able to do that" philosophy, which may work for regular users, but was kind of what I wanted to get away from by switching to Linux. Also OBS works poorly on GNOME (naturally the two projects blame each other for why), and really almost all of my general Linux usability problems went away after switching to KDE.

I tried i3 for a couple of days because I like the idea of tiling in theory, but I have 3 monitors on my desktop PC and I started getting really confused and frustrated about which "desktop number" was on which monitor and contained which applications. I think I could see it working a lot better on single monitor setups.