I don’t use WhatsApp since some years now and almost all of my friends have at least one other messenger; or I just use SMS/email in some rare cases.
My personal favorite is XMPP (clients: gajim on the desktop and Conversations on Android), because I think messaging is more than mobile messengers and I use it on the PC mostly.
I also use Telegram (insecure by default, but useful for groups), Threema (I like that it’s paid, so you know their business model; but push doesn’t work without Google Play services, so messages are late for up to 15 min) and Signal (most preferred after XMPP).
