Signal - moved my immediate family to it, and now have a few friends on there as well.

It had some rockiness maybe about 3 years ago, but with their new group implementation and some other small tweaks I find it just as easy to use as whatsapp, albeit it a little uglier.

#1 complaint is the coloring - incoming messages should be high contrast, outgoing should have the background color. For some reason signal does the opposite and it's hideous.