Probably depends on who your friends and families are but iMessage is super popular in parts of Australia. Facebook messenger is also quite popular with a lot of people I communicate with. WhatsApp is third for me, where I am in one group as well as individual messaging to to one or two people. It seemed to be getting more popular here over time but some people switched to Signal when WhatsApp made their privacy changes a year or so ago. Seems to have lost some momentum here, but again maybe that’s just my circles.