They seem to recommend DeltaChat over Skikket (XMPP) because of the better iOS app, but I think if you don’t mind that, XMPP is somewhat better as it handles group-chats better and the encryption standard used is also stronger. But DeltaChat is indeed a bit easier to use and there is no way to accidentally disable the end to end encryption with it.
Another advantage of XMPP is that it can do encrypted calls, where as Deltachat has no call functionality, it only offers video or audio messages that can be uploaded to the encrypted chat.
The QR code connection thing, encryption by-default combined with a reliable universal app that works on all platforms, and email being difficult for state-actors to block are nice features of Deltachat, though.
It seems both have their place at the moment. It’d be nice if XMPP could eventually adopt the good parts of Deltachat.
XMPP is similarly difficult to block as a lot of background stuff is running over it, like for example Android push notifications. A XMPP block on network level would likely also block WhatsApp, which uses the same ports and is still using a protocol very similar to XMPP.