Actually, I find the UI of git easier than Mecurial, but I think that's mostly because I try to make Mercurial work with the work flow I use for git and it just won't do it.
Since I grasped the idea of the index in git, I find it difficult to use any other VCS. The way git allows you to make changes to your source tree and then selectively commit them (git add -p) is incredibly addictive. The MQ extension in Mercurial tries, but ultimately fails because the underlying model doesn't support it.
Git has a really simple mental model, and all its commands are part of a toolkit to work on that model. Mercurial keeps telling me can't do what I want. Rewriting history is nice for perfectionists, and git's toolkit approach makes it possible for tools like Gerrit to integrate the review process seamlessly with the revision control.
IMHO Mercurial really needs to be able to support a Gerrit-like workflow before I'd seriously consider using it in another project.