Given that they’re both open source and can be customised using turing-complete languages, the only limit to possibilities is how much effort you’re willing to put into customising them. Even CVS has the possibility of working as a distrubuted system if you wrap it up in enough layers of hacky shell scripts ;)

Having done quite a bit with both mercurial (which the sapling CLI is based on) and git, I find that the mercurial approach has a lot more sane defaults, is generally less effort for the same results, and has a lot of quality-of-life improvements — like git has the possibility of doing interactive commits with `git add -i`, but sapling's interactive-commit interface actually makes it usable.