I choose Ruby! ex, my website: cookie clicker

I say ha ha...They are different, I would not being able to say which one is better. Both are fast, efficient with a big community.
Python is the obvious choice when it comes to computing and processing a lot of data. Ruby on the other hand will be perfect when you need a rapid prototyping of traffic-heavy applications.
Concerning web development, both Ruby and Python have powerful frameworks (Rails for Ruby and Django for Python). Ruby is popular and flexible with a very strong community always on the edge of development. Python's framework is preferred to create web applications and has the advantage of being easier to learn.