I’d say +1 for Qt if you want to create an actual GUI, since VTK is fully compatible with it and provide the interface for it, QVTKRenderWidget, QVTKRenderWindowInteractor.
That being said, recent improvement to VTK have recently been made so it can be used directly to create an application (eg: system logo, drag&drop, …), see F3D for an example. Creating actual menu and GUI in this context would be complex, especially cross-platform.