I don't use XMPP since the Google talk era, how are the available servers nowadays? Does they support federation, meaning that users from different servers can talk to each other?
I use it on and off to participate in a few small communities. It can sometimes be frustrating to find a server with the right setup for the clients I like to use, but when I finally do, I have no problems. I have only seen one non-federated server.
I can't speak for the backend, because I've never hosted a server myself, but I find the good XMPP clients to have many more features and to be much more performant than the good Matrix ones.
I can't speak for the backend, because I've never hosted a server myself, but I find the good XMPP clients to have many more features and to be much more performant than the good Matrix ones.