Briar

Signal.

Not necessarily because it’s better or because I like it. I actually don’t like it: Signal requiring a phone number really, REALLY doesn’t sit right with me, I hate not being able to back up my messages and having to hold the tiny button on the screen to record an audio or video message really sucks.

But it’s the easiest and most common of the truly private communication apps to get non-technical people to install.

Matrix but thinking about XMPP as Matrix leaks a loy of metadata and is pretty slow and new.

If we told just anyone, it wouldn’t be private!!!

Srsly any phone app is inherently insecure because the phone itself is insecure. And there’s lots of metadata leakage, like the phone broadcasting its location. There is no “go to app”. It all depends on what you are trying to do and who you are trying to communicate with.

Neither Matrix nor XMPP are software, those are protocols. Alsp, there is no point in specifying that XMPP is encrypted without doing the same for Matrix, since you can exchange plain text messages there too.

As for the actual question, here you go: https://www.privacyguides.org/en/real-time-communication/#criteria