XMPP is the best among the listed options, although ??? is not that far behind (or wouldn’t be, I still can’t find a mobile app, does anyone know one???). Good servers include Snikket, ejabberd and Prosody. It’s also the best fit for a small and/or private installation because it’s quite light (not lightweight like IRC, but still light), whereas Matrix is a nu-protocol and this quite hefty on resources, and honestly I have never seen benchmarks on what running a ??? service is like, not even for the official Docker container.