Delta.Chat is really underappreciated, open-source and distributed. I recommend you at least look into it.

Signal, on the other hand, is a closed "opensource" ecosystem (you cannot run your own server or client), requires a phone number (still -_-) and the opensource part of it does not have great track record (I remember some periods where the server for example was not updated in the public repo).

But yeah, if you want the more popular option, Signal is the one.