Matrix - Works well, but UX is too techy for my non technical friends.
IRCv3 - never tried.
Currently, I am using Tox P2P, so far it's working best.
I am looking for a web client because native clients don't provide me Telegram like feel.
So, if I find some time, I'll be writing my own web front end.
I am also looking to hire people to work on my Tox web p2p frontend.
The major messaging (and notification, if you believe the rumours) networks are all based on xmpp.
The issues are basically: big vendors want lock-in so they disable federation and spam. I remember seeing an XEP that aimed to solve the spam issue for federated xmpp.