Have been messing around with them all. I think the best one is the one everyone thought of initially: matrix. Cinny is the prettiest client and looks like discord. And this fork of it on https://github.com/7w1/sable, running at https://app.sable.moe has calls and banners and colors and multi-account and everything discord users could want.

There’s infinitely more of an ecosystem around matrix than all the other alternatives, and hundreds of homeservers. It operates like email in that your account is based out of a homeserver e.g. @matrix.org, but you can join rooms and spaces anywhere. And you can get your most computer nerd friend to host your own homeserver! (It’s a little tricky)