Facebook Messenger for friend and family that can't use SMS (or understand texting.) Google Voice for everything thing else. I really like Line, Quidd (don't judge) and Telegram. But I use them more as BBS services then a true messenger app.
What's quidd?
Franz on desktop. It uses 3GB of RAM and doesn't allow shortcuts to open individual services, but this is where we are in 2018. The slow death of interoperability has ruined messaging.
On my android: Threema, Slack, HipChat, Telegram, Hangouts & WhatsApp - this is the only option to reach 99% of chatting. In Germany / my list of WhatApp user is decreasing.
So what's the reason behind people flocking from WhatsApp?
In Germany, people are very concerned about ongoing data scandals on Facebook and this is one reaction.
IRC, and matrix. I use trillian5 with a custom skin as the client on my laptop, and riot on my phone.