I live in China, so I mostly use WeChat. It is a great app for the phone, unfortunately the app for mac sucks, as you have to use your phone to log in, and it, unlike the iOS app, does not have translation built in. But most of the other IM apps require a VPN, which I have, but is a pain in the *** to use constantly.
I use Facebook messenger sometimes to chat back home. Skype to call mom, because for some reason FaceTime can't ever seem to get the job done.