* XMPP is using addresses with the same format as e-mail addresses (Jabber ID/JID), Signal accounts are bound to your phone number
* Signal has strong end-to-end encryption built-in, for XMPP you need OTR or the recent OMEMO port of Signal's end-to-end crypto magic
* XMPP is federated, where you talk to your server, and it talks to your buddies servers; with Signal everybody talks to WhisperSystems' servers
* XMPP has no decent iOS app, but pretty good multi-device support otherwise
* XMPP is using addresses with the same format as e-mail addresses (Jabber ID/JID), Signal accounts are bound to your phone number
* Signal has strong end-to-end encryption built-in, for XMPP you need OTR or the recent OMEMO port of Signal's end-to-end crypto magic
* XMPP is federated, where you talk to your server, and it talks to your buddies servers; with Signal everybody talks to WhisperSystems' servers
* XMPP has no decent iOS app, but pretty good multi-device support otherwise