The decision is made! I've selected a DVCS to use for Python. We're switching to Mercurial (Hg).
It's hard to explain my reasons for choosing — like most language decisions (especially the difficult ones) it's mostly a matter of gut feelings. One thing I know is that it's better to decide now than to spend another year discussing the pros and cons. All that could be said has been said, pretty much, and my mind is made up.