stupidcreature it does not matter which Matrix client you use, ... Anyhow, none of that matters since the protocols Matrix uses or the developers are not particularily trustworthy.
It does matter. Element doesn't use the libolm library mentioned in that blog article, for example, but uses one that actually is correctly implemented and secure. Some lesser known Matrix clients might use libolm, however.
stupidcreature Session could be better due to being a Signal fork
Session is not a Signal fork. They have implemented a version of the Signal protocol where they have intentionally weakened the cryptography substantially, to the degree it is no longer possible to guarantee the protocol is safe. It is not known broken either, but intentionally weakening the cryptography does not witness about taking security seriously.
stupidcreature I am not aware of any gripes with SimpleX, but nonetheless, Signal is tried and tested and Molly is a great client for using it.
Signal is the most trusted messenger, with pretty strong security proofs too. SimpleX seems to come at a second place right now, despite being entirely new. None of Signal, SimpleX, Element or Session are poor choices though.
stupidcreature The best answer to this question may be Cwtch.
Never heard of. And that is usually not a good sign, since I am pretty knowledgeable about the reputable messengers, and privacy sphere in general.