it is a lot better
Developing for QT is a bliss for a C++ developer.
Every single aspect of it is so well documented that you really envy it, because you know that you will never document your own API that good. Even code adaptation between major releases is made easy to do due their clarity on explaining every single change thoughtfully and with great didactic.
Their API itself is quite a work of art, a show of well wrote C++ OO code.
That being said, QT is locked in C++. It don't have anywhere near the same amount of language bindings as GTK. I believe that this is due QT's overbearing nature, since it is a tad lot more than just a GUI toolkit, so creating bindings to other languages is a difficult task without a fairly large team.
Indeed comparing QT with GTK is quite unfair from a developer POV. QT is a application framework that happens to have a GUI toolkit geared towards creating multi platform applications, with a SQL framework, XML parsing framework, network bindings, thread API, multimedia API to access camera, soundcard and mic, a event system that extends way beyond GUI... while GTK is just a GUI toolkit and nothing more.