LWN.net has an interesting article about how Emacs chose a new version control system: <http://lwn.net/Articles/272011/>
They were back in the CVS stone ages, but their main contenders were the same big three of distributed VCSs: git, hg and bzr. The article pulls out a couple of very good quotes from their discussion. The one that caught my eye was from Richard Stallman: We already know the most important thing about what we will find from a careful study of git, mercurial and Bzr. We will find that each has its advantages and disadvantages -- but none of them conclusive. Each will be preferred by some people, but any one of them would work out well enough. - R.