There are better alternatives but all people utilizes Whatsapp...
A lot of people have started to use Telegram
In Germany Threema is also popular.I stopped using WhatsApp when it was bought by Facebook. But I rejoined, when they introduced the encryption. Most people have it, so it is something like a standard.
But I also use Skype and Telegram
In Brazil only Whatsapp is used.
Telegram also, mainly in corporates!
In Venezuela it is widely used by the Free Software and Open Source groups