Secure (knowing but not being able to access) being different from privacy (no-one knows who) and of course remembering that the more private especially, the more difficult to locate anyone you actually know as zero e-mail, phone numbers, etc should be used… I’d still say Matrix is the simpler and easier secure messenger for most to use and where they have a good chance of finding others actually using it.

Can also mention Wickr Me, Wire and Threema. Briar Project would have been a good option except it is only Android which really holds it back from broader use. Another consideration is whether mobile to mobile is satisfactory (peer-to-peer is sometimes an issue with mobile) or whether you would use desktop clients along with mobile, as that then also narrows some choices. From a privacy perspective, specifically metadata is important and why Signal and WhatsApp fall down even though they may have secure E2EE.