@michaelharley if you want to get positively surprised, go for Delta Chat, server is super cheap to host and require the least maintenance of all that options you mentioned
it is also the only one of those that has multi-homing meaning people don't depend on your server and can use several at the same time or migrate away of yours etc. meaning even if your server goes down or during maintenance time, they can keep receiving messages etc.
it is also the only one of those that is if you fucked it up and wiped the whole server, can automatically recover without the users even noticing (you don't even need server backups! because there is no groups etc metadata in the server and accounts are automatically re-created on login)
you don't need to worry about storage and account management, accounts get created and removed automatically, storage is removed automatically as well and by default the clients will also delete messages immediately from server after downloading them
it is also the one with the most user-friendly interface and cohesive experience across platforms, the one with the best pain-free multi-device support that just works
in xmpp the group depends on the server, if the server is gone the group is dead, in matrix a lot of group metadata is on the server and reactions are not even encrypted
read here: https://elk.zone/fosstodon.org/@arcanechat/115963841644398921