After it became clear that darcs wasn't going to win the next gen source control wars I switched to mercurial. I now use and love git for its own charms, but I'd love to come across mercurial again professionally.
I own up to my preference to rewrite history—git has facilitated that in equal measure to mercurial—but my first source control love is mercurial queues. Queues taught me how to structure and sequence my changesets, and through that the structure of codebase evolution. The user experience is still unmatched by any patch queue on git.
It's worth looking at hg-git. It works brilliantly --- seamless interoperability between hg and git; you just tell hg to clone a git repository and it Just Works. Merges, branches, tags, the lot, but with sensible commands and workflow.
There are a few rough edges; creating a new branch (git branches are mapped onto hg bookmarks) is a bit clunky, and it's easier to create the branch at the git end and then do an hg pull to get all the metadata set up, but I mainly use it with github and github's UI for handling branches is pretty good.
I own up to my preference to rewrite history—git has facilitated that in equal measure to mercurial—but my first source control love is mercurial queues. Queues taught me how to structure and sequence my changesets, and through that the structure of codebase evolution. The user experience is still unmatched by any patch queue on git.