It seems like everyone is converging on 2.7. The commercial distributions from ActiveState and Enthought are at 2.7. Apple's OS/X Lion ships 2.7. The major linux distros are there. PyPy is at 2.7. Jython and IronPython are mostly 2.7 capable. And my understanding is the Google's AppEngine will be at 2.7 soon enough.
This is the Long Term Support version of Python, the one that is currently getting bug fixes and will continue to get bug fixes long into the future.
AFAICT, there are very few reasons to be using an older version of Python. By now, most of major third-party modules are working with 2.7 so there shouldn't be much holding you back.