1. wxPython has inconsistent looks and layouts between platforms and monitor resolutions (or DPI). For example, on PlayOnLinux GUI app I cannot click an "OK" button while using Surface Pro because the button is hidden outside of the window.
2. QML is an amazing language. It is modern, declarative and reactive but still very simple to use. Personally I don't want to go back to the traditional GUI coding styles after experienced QML.
3. Qt Designer is a great GUI tool that you can quickly prototype a GUI app.
4. Qt has the best documentation among cross-platform GUI frameworks.
5. Qt is a much bigger framework having more features. For example, you can easily embed WebKit or Chromium very easily.