I've done projects with both, and I think git, once you get over the learning curve, is much easier to work with and get things done.  With mercurial, I always feel like I am fighting the system to make it work.  With git, the only struggle is learning the right commands, and then once you do everything just works perfectly.  I think the git staging model is really nice, and I git stash can't be beat.   If you are working with a lot of branches or want to work on a lot of separate issues at one time (develop features, fixes or support issues separately in parallel) git is so much more pleasant.  Mercurial isn't bad by any means, but git just gets more things right, IMHO.