It depends on what you are willing to do.
Python 3.0 is the newer release, and with time should become the standard.
However, it has almost no libraries or frameworks available, and even the tools are not so up to date (e.g. the Eclipse plug-in for Python is still in the migration phase).
On the other hand, there are no huge differences, and once you learn one, moving to the other is quite easy.
So, if you plan just to play around, you can go with 3.0.
If you plan to use it on a new project, I would stick on an older release.
