I want to create a somehow complex application:
It is a game level editor. You can put in tiles and other objects for a level. Then "compress" the level data into a file.
With another application, it will read the file's data and play the game.
The application is for Windows mainly. Other platforms are yet to be considered.
So I need help deciding:
If you were to do something like what I described, which programming language would you choose?
I want to decide between Ruby or Python.
I want you to help me choose depending on my following needs:

Easy GUI platform for making the editor.
Can show sprites, move, transform them etc.
Can play audio.
Can compress data, graphics and audio. The compressed file can only be read by another application I make.
I've never used Ruby but I'm sure there is virtually no difference between the 2 when it comes to libraries.  I know what you want can be done with Python using wxPython or pygame (or the combination of two).  But I'm sure there are similar libs for Ruby.  So just look at both languages and use the one you like better.
Making a somehow complex application: Ruby vs Python