We all know Signal, Matrix, Telegram, SimpleX, etc… But if you can’t access the internet you can’t communicate. Pretty logic. But would it be possible, at least theoretically, to create an app that permits to message people even if the internet goes down?
It might be a dumb question I really have no idea to be honest.
Honestly if you don’t want to think too much about it, go with Briar, it’s way more battle tested, while Berty seems like it hasn’t seen much adoption since it’s younger, both have a bit of development activity I saw, so I can’t say if one is more or less maintained than the other
As for the actual question of gauging which has the better cryptographical implementation, I don’t know either, beside the most surface level information I know very little.
I believe if you want to look into it, you’ll have to start from their whitepapers