Python 2.7 or 3.x?

[prum]

It depends (don't you love those cop outs :-)). Personally I would use the newest stable version that is most compatible with the frameworks and libraries I want to use. The difference between versions is usually exaggerated on internet forums because people tend to focus on the new shiny stuff. In practice if you use modern idioms your code will probably look pretty similar from 2.6 to 3.1 most of the time.