WhatsApp has two further disadvantages (to dinosaurs like me who only play PA on a PC) - it has no desktop app (so an Android emulator is needed) and it requires a valid mobile phone number to activate the app *.
I find TG the most "useful" (and PC-friendly) of these "new" com systems and I have used it, WA and Slack over the last few rounds. (I still prefer the IRC options. Slack allows an IRC server to be set up and TG allows bots to relay to netgamers channels (as does Slack)). WA is my least preferred option.
* I do now have a mobile phone but it lives in my car and is used in emergencies only (needing a mobile broadband signal counts as an emergency).
Only my close family members are allowed to know my mobile number.