I want to develop a Windows application. Honestly I care little about cross-platforms for now (but still would be good)

I want to use Ruby, since it has quite a simple syntax and is so.. well, simple and easy to learn.

My application is like a "game level creator", where you can design your own level and then run it with another application which is a "game level player" by reading the project file created by the creator app. You get the idea.

Now, I got a new PC and is completely clean. Absolutely no trace of my old Ruby experiments and fails.

First of all, I will need to choose a GUI platform for my Ruby application! Can you recommend me one? I have heard of Shoes and Tk, but want to know what you think.