I have an application whose GUI is to be remade for ergonomic reasons.
It was written in PyGTK and I am wondering if I should switch to PyQt to ease future developments or not.
This application has a mostly classical UI with buttons, toolbars, dialogs etc. but also has some specific requirements : I will certainly need to create a custom widget based on treeview/tableview (to make a spreadsheet-like widget) and this application has a lot of worker threads which update the GUI.
I am seeking advice on these two points :

As regards the creation custom widgets, does PyQt provide better mechanisms than PyGTK, especially to slightly modify existing widgets.
I had problems with (even when properly using threads_init() and threads_enter()) the updating of the GUI by worker threads while using PyGTK. Is PyQt any better on that point ?
Definitely PyQt... There are a lot of advanced applications using it... Personally, I'm using KDE, so, even my system's GUI uses Qt! I'm also creating a spreadsheet application and I find that it's far easier that what I thought at first... But, BiaXpirit is also right: except if you're developing an open-source app, maybe you should use PySide or something else...
What are the advantages of PyQt over PyGTK and vice-versa?