Most likely both, since different social groups in different countries have settled on different messengers. E.g. In Europe/Israel it's Whatsapp, but in eastern Europe and ex-USSR it's Viber (for older people) and Telegram (younger people), almost nobody uses Whatsapp.

Speaking about preferences (and excluding privacy question because I have no expertise there) I would pick Telegram because while on mobile it is essentially the same as Whatsapp, desktop client for Telegram is miles better. Whatsapp client was crashing constantly and regularly, every few days. It's just junk.