The best messenger to use?
For newbies I recommend Signal, although I highly dislike that it requires a phone number to use.
Threema has to be by far my #1 choice for a messenger. No information required at all to use the app. Threema is paid though. (one time fee)
SimpleX Chat is newer to the messenger game, but packs great potential. It gets the job done fairly great, but I have had some smaller bugs with it that need some time to be perfected.
Session is another good one that is free and easy to use, but I have had heavy sending/receiving issues in the past to proceed with caution.
Element (formerly Matrix) is a popular one that is somewhat similar to Discord but I never personally got myself to like it.