XMPP looks weak
Discussion
It's a different model. XMPP assumes you trust the VPS operator (or it's you).
SimpleX assumes you don't, but also that not everyone is self-hosting among friends
if SimpleX is easy enough to self host, I think it's the clear winner
I like simplex, but your messages are split, so you don't pick which relay the person you're talking to picks.
also there's issues with phising and proving identity. He's going to add PGP verify within the app, so hopefully improvements on the horizon