Currently using Signal. If Canada passes Bill C-22 Signal will leave so I'll have to find another messenger app.

SimpleX seems like a good one. Doesn't use Google notifications which is great for degoogled devices. Set it to check every 10 minutes instead of constantly and it's very easy on the battery. Messages come in right away if the app is open, such as when having a conversation with a contact.

Edit: SimpleX is also very easy to use, as simple as Signal. This is important to get non-tech people on-board.