If you're doing something completely new that will never interact with older code bases, Python 3 seems like the best choice. This is where the language is ult

If you're doing something completely new that will never interact with older code bases, Python 3 seems like the best choice. This is where the language is ultimately going. However, if you have to integrate with almost anything in 2.x land, such as 3rd party libraries, you may have no choice but to keep using 2.x for awhile. As usual, even from this older version, there are ways to voluntarily import future capabilities so that your code is as 3.x-like as possible.