Delta seems cool, I haven’t used it much, but I would rate it one step below Signal for general use. It can be the chat for 30s, I think 😀

Signal is better than WA (from privacy point of view) but it’s still a centralised service. I am personally a fan of xmpp but since I was never even able to convince anyone to switch from WA to Signal, convincing people to switch to a federated service is even tougher.

On the other hand, switching messengers once every decade should be fine, I think. We did switch from ICQ/AIM to Yahoo! / MSN messenger, then came Skype, then WhatsApp. I think Signal should be good enough for this decade.

There’s also Threema, Swiss based, but it has one-time payment, so most people wouldn’t like it.