So, I have a Threema license, but from what I’ve seen its encryption isn’t post-quantum. Signal’s encryption seems the strongest. I host my own matrix server.
Also, I kind of don’t care where the servers are or which provider it is. Everything is encrypted anyway.
I prefer signal because it’s been the easiest one to convince my friends and family to use. I have like 8 friends on Signal, the 1 I got onto Matrix quit after a week. Matrix I treat more like foss Discord so I only use it for communities. ElementX is really nice though so I have hope that eventually it could be as smooth to use as Signal.