They will both probably be about the same, tbh. People seem to like Qt a bit more, but high-quality bindings really only exist for c++ or python. GTK, on the other hand, has bindings for most langauges. You could also use tcl with tk, java (or clojure or kotlin or scala or...) with javafx or swing, d with dlangui...

Ultimately, what's important is to start making something. Any language, any toolkit, doesn't really matter all that much. If you don't like it, try another language, another toolkit.