I think those two things that arxanas mentioned are the biggest differences (i.e. working-copy-as-commit and conflicts in commits). I haven't used Sapling, but I suspect Jujutsu has better support for moving commits (and parts of commits) around without touching the working copy.

Sapling, on the other hand, has much better support very large repositories, since they've spent a lot of time on that over the years. We're going to copy some of Sapling's solutions to Jujutsu soon, since we're working on integrating it with Google's monorepo (slides: https://docs.google.com/presentation/d/1F8j9_UOOSGUN9MvHxPZX..., recording: https://youtu.be/bx_LGilOuE4).