Gnome. I actually started with KDE. It's a good DE, but it's got so many options that I had choice fatigue. I constantly tweaked my taskbar instead of focusing on what I wanted to do. And it was easy to get it to a "looks broken" state
When I tried Gnome, I fell in love with it. I love the unique workflow, lack of distractions, the modern adwaita design, etc. Everything felt so polished
That being said, I don't like how Gnome devs seemingly can't agree on anything with other desktop environments. And I don't like how they refuse to support server-side window decorations. Like, I agree that CSD are better than SSD, but it would be reasonable to support SSD for toolkits that haven't/don't want to implement CSD themselves, right? Well, Gnome devs in their infinite wisdom disagree
I'm excited for Cosmic. It looks like it combines the best of Gnome and KDE, and the devs don't have the “my way or the highway” mindset