Python, Lua, Ruby, or Scheme for Game Prototype?

I had an interesting idea for a casual game and was planning on prototyping it, but now I'm stuck on choosing a programming language to do so. I've had luck with Python and Pygame before, but for some reason can't get it to work on Vista.

Both Lua and Ruby look promising with active game/SDL libraries, but I keep thinking that they won't meet the future needs of the game if I take it past the prototype stage. Lua's lack of an object-oriented model bugs me, but I think I could get around that. Performance is also a concern, though. Ruby is definitely getting better, but I also need to understand how far I can push Ruby's for dynamic class members, and the online docs aren't so hot. Also for either one I'll probably need to learn how to write extensions in C to implement some of my ideas.

I'd really like to pick Scheme, but the game support is poor for existing implementations, as is the final distribution model for those that aren't compile-to-C. I have a half-built Scheme implementation from a while ago that would be ideal, but then that's yet another distraction from really getting to the prototype.

I have a feeling I'll start with Ruby and move to something else as necessary. I initially avoided Ruby, but now that I'm taking a closer look it seems pretty good for this type of work.