WXWIDGETS also has some designers and documentation but not so good as in QT . wxWIDGETS is relevant for writing portable desktop applications with a native look and feel nothing much has changed there wxWIDGETS , worth as our primary GUI framework to work with . wxWIDGETS is easy to use but still powerful and programs made with it can easily be ported to windows , mac, linux, and several other platforms, allowing your programs to reach more people. Not much is required for this tutorial besides basic knowledge of c++.
IT depends on your background and what you want to do with tghe newly acquired knowledge. If you want to write commercial applications but don't like to pay for developer licenses go for wxwidgets .
If you want a maturer and easy framework that is quite well documented and has a great cross-platform IDE
I think QT would be better. Because I use QT exclusively for GUI Applications.
QT is a framework which includes much more that two GUI technological .
The QT framework include cross platform multithreading .
Support for XML and JSON .