How does wxw and gtk roughly compare? I have liked the UI of Audacity moderately more than Inkscape, but I don't know where framework versus implementation is at play.
wxWidgets uses whatever GUI functionality is native for each OS instead of implementing its own (though there is also a wxUniversal backend which does its own controls but i'm not sure how complete it is). On Linux wxWidgets can use Gtk, Qt or Motif (though Motif doesn't seem to be tested much and while it does compile and work, there are a bunch of bugs).
I was with wxwidgets now switching to gtk, as the latter is way more widely used, wxwidgets is native looking for each OS, gtk has its own appearance, both shall do fine.