Personally I like XMPP over Matrix because
- Matrix clients aren't great (even element is buggy as piss on my phone and a shitty electron app on linux)
- Matrix is too difficult for "normal" people (I agree they should get good but they don't and what good is a chat app without recipients).
- Matrix public rooms have a CP problem, and as such I can't recommend people join it just in case, I don't need my mom seeing that shit.
- Matrix was started as an Amdocs project before they defunded it and the lead dev went to form The Matrix Foundation. Amdocs is a Mossad affiliated company that infiltrated American telcom companies long ago. Matrix also pisses metadata to any server it federates with, including matrix [.] org, and I have no proof that Mossad is spying on that metadata but I have no trust either, nor proof that they aren't, so I can't trust matrix anymore.
Though XMPP also has had it's own problems for me, so at the moment it's my fallback and I'm trying out Delta Chat which I have been loving.