Depends on your experience. If you know C,C++,Java and the whole C-syntax-bunch. I'd recommend Python just to learn to adapt a different syntax. If you want to learn for the learnings sake, i'd also recommend Haskell to try functional programming, if you do not already know it.
Ruby has some interesting concepts, Python (well CPython) does not have. Blocks for example, which make Continuations possible. In Python you need stackless Python (a different implementation) to do this. -- http://mail.python.org/mailman/listinfo/python-list
