In my obviously biased opinion, the advantages of wxWidgets are:
- Native widgets (as far as possible) guarantee native look and feel
- Standard C++ only, no special preprocessor/extensions
- Possible to link statically to closed source applications without buying a commercial licence
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.