Matrix is riddled with bugs. While I agree with you that signal isn't all that great (they do some really good stuff and then make some really weird trade-offs), I've recently compared Signal, Wire, Threema, Jami, Briar, Element/Matrix, and Keybase.
The most mature app is Signal. It has the best usability to privacy trade-off.
Threema is the better choice if you don't mind not having a usable desktop client. For me that's a total deal breaker. It costs a one-time 5 bucks and it's totally worth that, if only it had so much as a usable web client (you need to open your phone and navigate two menus to enable the web client every time your phone changes WiFi or anything).
Wire is the better choice if you can sacrifice a tiny bit of usability for better privacy. It's sluggish is all, and (like Signal and most other services) uses AWS. Full disclosure: I was involved in a paid audit of Wire so I know more about the encryption protocol than I do about the other clients'.
Element/Matrix is the better choice if you'd rather make a trade-off towards privacy. Presumably the clients will mature, and between two years ago and one year ago they've made good progress. It's going less fast today but I still see things getting slowly better, and the decentralization works very well and fairly easy to setup.
If all you really want is a better privacy policy and want to ensure people stick around and don't uninstall it, Telegram is by far the usability winner and has a large network effect already. But it's a trade-off with the devil because there is zero encryption. They could ransom or sell our chat logs any time.
Briar and Jami have limitations that make it unusable for general purposes use with your mom. Facebook and Google's messengers I didn't look at for obvious reasons. Keybase was never end to end encrypted to begin with and now Zoom bought them so they'll probably shut down soon (also, bugs).
Rocket.chat seems only aimed at business users.
You can also do OTR over any platform you like, and I still have to try this overlay encryption system on Android (I forgot its name).
Pick your poison...