SimpleX is quite a promising project, uses Double Ratchet End-to-End-Encryption (from Signal), and has a very interesting protocol and model to provide quite strong metadata protection, especially in regards to whom you talk to and groups you’re in.

If your threat model requires exceptionally strong Metadata protection, SimpleX is probably going to be your go-to

Though, for a more lenient threat model, where still good, but less laser-focused metadata protection is enough, Signal will probably do just fine.

Personally I use Signal, but I also have a SimpleX Profile, an XMPP Account and Matrix. (preferred in that order)