I prefer Mercurial because is much easier to use but this file rename issue always make me feel uncomfortable when reorganizing code.
These days I'm giving Fossil a try, which still is easier to use than Git and the repository size sits between Git and Mercurial.
Git is not hard to use. It is adding a few articulations in your workflow, and they are just allowing you to run faster.
One example: interactive staging with git add -p, this articulation masks it much easier to debug: add print all over the place, try some tweaks, find the one, stage this one snippet, checkout the files, run the test, and you're done.
Even if this larger project could handle that bandwidth, it is a significant factor for smaller projects, or larger projects like github. Meaning more of a chance that git remains the dominant choice.
edit: quick speed test, git clone from my server = 17.4 seconds, hg clone from the same server's hg repo = 25.4 seconds
Both Git and Mercurial use hardlinks for local clones by default, so the reason why Mercurial is slower than Git for local clones is primarily that its repository data generally contains more files.
Cloning/pulling/pushing speed across a network is in large part determined by the protocol used; a few years ago, Git's network performance was inferior to that of Mercurial [1]. I believe that has been largely fixed since then.
Finally, Mercurial allows you to have local feature branches that you can delete if they are abandoned just fine.
[1] https://code.google.com/p/support/wiki/DVCSAnalysis -- footnote 1
Another data point: when we converted to Git, I did a number of speed comparisons. Our repository was 77MB in Git versus 178 MB in Mercurial. Clone time from bitbucket over either (smart) http or ssh was 18 seconds with Git, versus 2 minutes with Hg. We can do a shallow clone (--depth 1) in 4 seconds (10 MB transferred) with Git, but Hg has no comparable feature.
[1] I find both Mercurial and Git adequate, but lacking in some aspects that are important to me (both with respect to architectural design and workflow considerations). For practical work, I consider the differences between Mercurial and Git to be relatively minor in comparison and cannot really get exercised over them.