About GUI Framework compatibility

Hi, I'm starting an application and I'm considering developing it using C#, Mono and OpenTK. The main downside is that the application requires an "attractive" GUI and I need to support both Windows and GNU/Linux, Mac OSX is not a must, at least for now. I started to investigate what GUI Frameworks exist for Mono, and found this:
http://www.mono-project.com/Gui_Toolkits

So I wanted to ask the OpenTK community directly, how is OpenTK support for these Frameworks. I know there's a Windows Forms and a GTK# widget, but I don't know how reliable they are, and since I have C++/wxWidgets/Qt background, I would also like to know how supported are wxNet, Qyoto and Qt4DOTnet.

If anyone knows of another GUI framework, do not hesitate to recommend it, specially if it works directly with GameWindow.