GTK3 has a very small adoption rate for cross-desktop/OS applications. Except for the gnome DE (which I'm not using), on my system the only two applications using GTK3 are wireshark and lightdm. Heck, even GIMP on Debian is still using GTK2.
QT4+ is faster than GTK3, the API is superior in almost every respect, has better cross-platform OS support. It should be telling to every user how some basic widgets like the file-open dialog in GTK3 has actually regressed in every respect compared to GTK2, and many others actually behave worse from the user's point of view (which should be the #1 priority of any widget system, even before the API).
I used to prefer GTK for the footprint (and mind you, I was always aiming at pure X11 development), but not anymore.
QT4+ is faster than GTK3, the API is superior in almost every respect, has better cross-platform OS support. It should be telling to every user how some basic widgets like the file-open dialog in GTK3 has actually regressed in every respect compared to GTK2, and many others actually behave worse from the user's point of view (which should be the #1 priority of any widget system, even before the API).
I used to prefer GTK for the footprint (and mind you, I was always aiming at pure X11 development), but not anymore.