The question has been asked before, but the most recent one seems to be from two years ago, so there must be new developments that must have occurred in the two toolkits.
So which toolkit should I use for developing a GUI with C++? What are the pros/cons of each?
In my obviously biased opinion, the advantages of wxWidgets are:
Also, whether it's an advantage or a disadvantage is up to you to decide, but wxWidgets is primarily a GUI library and seeks to play well with the other specialized libraries (like SOCI or asio, for database and network support, respectively) instead of trying to be the one and only true library for everything.