Having used both and others as well I must say I still like GTK as a user the most. But I would like to have them better interconnected. It's possible to theme each other supposedly though I only manage one way always gtk apps as qt.
Freedesktop should specify all these things so that irrelevant of the toolkit it would be the same data in the end.
I prefer to pay for a copy of a Free Software (FOSS) for it evolves than pay for a very restricted licence for only use a proprietary software.
People say Open Source is about freedom. But unless you know C++ you are pretty much screwed