Just to be completely up front: I am leaning towards hg for most of my own personal and work related stuff mostly because of its simplicity.
The most important point for me is that both these systems allow developers to maintain a history of changes in their own off line “sandbox”. This is a huge advantage where people often work off site, and even off grid.
In the end what’s really key isn’t what you commit your code changes to so much as that you commit them at all.
Analysis of Git and Mercurial. Internal analysis that supported decision to use hg for Google Code.
Mercurial vs Git: Why Mercurial?. Pro hg piece by product manager for products based on hg.
Mercurial vs Git: It’s All in the Branches. Pro git article focusing on superiority of git’s branching support.