Based on what I know, in a nutshell, Signal is centralised and requires phone number (both of which may not be ideal), SimpleX is decentralised (not one central server) and doesn't require phone number, Jami and Briar are peer-to-peer networks (but this means that both users must have the client running to receive new messages/notifications, which is not ideal). Signal seems to be more audited in terms of security and such compared to the smaller fish (but that's because it is a much, much bigger fish). For me, I would go with Signal since my threat model isn't super high, and it's much easier to get others to switch to it. SimpleX is a decent option if you don't want to share your phone number I guess, but it's more obscure and less established compared to Signal (in terms of users and security audits). Jami and Briar don't seem all that great for the everyday user due to the limitations of the peer-to-peer model (needing both clients running at all times drains battery it seems), but could be decent options if your threat model is super super high

Matrix is another option but is a bit complicated to set up, and unless you know how things work, it can seem quite confusing. It's more of a Discord competitor with the different communities and rooms.

Do you know deltachat? I think that one hit a sweet spot in decentralization.

https://eylenburg.github.io/im_comparison.htm