I'm a C# .NET developer and I work on mostly ASP.NET projects.
I want to learn a new programming language,

to improve my programming skills by experiencing a new language, 
to see something different then microsoft environment,
and maybe to think in a different way.

I focus on two languages for my goal. Python and Ruby.

Which one do you offer for me ? 
Pros and cons of them on each other?
Is it worth learning them ?

EDIT : Sorry I editted my post but not inform here, 
Ruby on Rails replaced with Ruby.
Rule of thumb - Python if you like strict rules and Ruby if you hate them. 
Another one: if you adore JavaScript - Ruby is your choice :)
Python or Ruby for a .NET developer?