Like many said, signal is centralised and requires a phone number.

Meaning it's not anonymous and the server owners can technically sell your metadata, not the content of the messages but who talks to who, what time, the length of the chat/call etc.

Either-way having to use a phone number to register an account, for me is not acceptable for several reasons besides privacy and metadata.

On top of that, the server side of signal isn't free software (as in freedom), which means that the whole program requires non-free (as in freedom not beer) network services in order to work. Which isn't acceptable for free software advocates.

Alternatives:

Simplex: If you don't require voice calls there are more options available there are many text messages, but very few support calls, which for me is a critical feature.

In theory Simplex is the best, it's e2ee, quantum resistant, each chat (message queue) is it's own "account", each "account" is just a private key, and you can switch servers with the tap of a bottom, it also supports private routing, which from what I understand is like some sort of onion routing between simplex servers.

Hosting your own server is also extremely easy, (tho note that running your own server can actually be detrimental to privacy depending on your threat model), supports calls, group chats and all the features I would ever need.

Unfortunately at least for me and my contacts, SimpleX it's terribly buggy, specially on phone, literally tonight I missed the opportunity to be with a friend because I only saw the message one hour late.

Very often messages just stop being received until the app is restarted, usually I have my friend send me a message via other (centralised) app in order to warn me that he messaged me, I also do the same for him. After restarting the app it usually works fine for a while until it does it again. And needs restarting again.

On top of it, it's taking more and more time to get the first message when in background even during normal operation, tho I blame Samsung for this one and not Simplex, and understand that Simplex doesn't use push notifications for improved privacy, but it has become a real problem, what used to take 5 minutes now sometimes takes more than half an hour. Maybe my phone is overloaded, idk.

Calls could be improved too, takes several tries for it to actually work, and it doesn't help when the other person calls me back and I call them at the same time.

On top of it, the volume of a call seems very quiet compared to a normal phone call and it's very hard to hear the other person, I'm guessing a simple compressor DSP could fix this.

Unfortunately also has been news of Simplex planning to enshittify the app with cryptocurrency, something that I politically and morally oppose.

Session:

I've used it for a month years ago, before I knew about SimpleX, whatever technical merits it may or may not have, (and from what I understand it's privacy is still below SimpleX) it relies on some cryptocurrency network in the background, so I won't use it. Self-hosting it also seemed to me no easy task, but I could be wrong.

Jami:

Never got it to work.

Matrix:

I haven't tried Matrix yet, I think I read long ago that calls aren't e2ee tho that may have changed now. I also read that Matrix leaks a lot of metadata which can be a problem. Maybe not if you self-host, but self-hosting comes with it's own privacy problems. Maybe I should research it again and try to self-host it and see how it goes.

So as bad as Signal is, I can't give you a working alternative, I put all with Simplex despite all the bugs but I don't think most people are willing to go though it, however if you (and your contacts) have a high end phones maybe it works better. But it's not something I can recommend.