However, most of the best apps are based on GTK and not QT.
Yes, I couldn’t agree more. Qt is nice, I use it in my professional work. But for me personally, Gtk is the best toolkit, and this is largely because it is programmed in C, not C++. Also, Gtk has the GObject Introspection framework which allows for other programming languages to connect to the Gtk libraries, so you can code Gtk apps in pretty much whatever language you like best.