Deltachat has an extremely smooth on boarding process and is the same app for all platforms, but it cannot do voice calls or screen share (you can leave voice messages though).

Jabber/XMPP generally has a less smooth UX, and different apps across different platforms (except the Movim client, which is a web app that works on all platforms, but doesn't do reliable notifications on mobile).

With the Movim client, Jabber/XMPP is basically a complete Discord and Signal replacement. It can do group video calls, screensharing with audio (only with chromium based browser for now), as well as voice and text channels under different servers.