Based on time spent using them, Firefox, Steam, and Terraria. Wait, do games not count?
The real answer is actually probably Gnome itself. The DE, I mean. The workflow suits me perfectly, and I even like a lot of the basic Gnome apps, although their naming convention get on my nerves sometimes (your official web browser is called "Web" and your official music player is called "Music"? But the one that makes me actively angry is calling their official text editor... "Text Editor." C'mon, folks.)
This has been the case for me since Gnome 3 dropped. Which was quite a surprise for me since I thought of Gnome 2 as a less user friendly, uglier XFCE and kinda hated it. I still kinda feel that way about Mate, but Memo kicks ass and it's much better than Gnome 2 was overall.