One more point I'd add to (2): given its massive inertia / network effect, the tooling and the resources are leagues ahead of everything else. I'm using Darcs for a few personal projects and while the core ideas are great, the tooling is just worse. From the ways to customize the diff utilities to use, to integrations with text editors (the vc-darcs module for Emacs is pretty barebones, especially compared to Magit, but even compared to the basic vc-git).