I know, I know, this is the emacs vs. vi debate of our age, never to be settled and pointless to continue arguing. I'm going to write just a little more about mercurial as compared to git (or git as compared to mercurial, whichever is less inflammatory to say) because today I realized something and I need to write about it.
I've been using mercurial daily at work for a good 5 years now and not much git. I recently had cause to use git a little more and I realized something. The common belief is that git is Freedom and mercurial is tightly constrained Bondage. I think that is mostly based on a very outdated understanding of how mercurial works and what you can do with it. Today it has all the same commit and history editing functionality of git with record, amend, graft, rebase, histedit, and so forth commands built-in. Mercurial is not missing flexibility and freedom enhancing functionality that git has, as far as I know. The thing I realized is that today's mercurial actually has more freedom and flexibility than git. Using git I felt like I was being constrained to work in the way Linus does. For example, I really don't feel the need for the index, especially when you are able to amend commits or do all sorts of other editing of commits with rebase, yet, there's really no way around it, with git you have to use the index. With mercurial you can choose to have index-like functionality, or not. With git you have one way to keep track of branches, using the reference-like things that git calls branches. These come with all the complexity and confusion of remote tracking branches and local branches and fast-forward merges (that are not really merges) and so forth. With mercurial you have three choices for keeping track of branches, a couple of which are much more simple and easy to use than git branches. I like having these options.
I guess I can't think of anything else right now, both tools are very similar in functionality and both offer far, far more freedom and power than any other version control tool that I know of. I'm sure git users will comment and tell us where git is more flexible than mercurial.