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.
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.