Here is a comparison between the two that will help you decide which one is better for you or if it’s worth switching to a different messaging service.
To begin with, both messaging apps are free of charge. All that they require is a stable internet connection which means that you can use them to call somebody from a Free Wi-Fi spot and not have to pay for anything. Secondly, there is the security issue. Out of these two apps, WhatsApp is believed to be the most secure one so far because it offers end-to-end encrypted messages. This implies that only the two parties engaged in the conversation can see the messages.
Viber offers end-to-end encryption as well, but it only works if the two people engaged in the conversation are using the same Viber version. This is why all of its users should update to the latest version as soon as possible.
Lastly, there are the issues related to video-calling which is becoming an essential tool in communicating with friends and family. Viber does offer this option for both Android and iOS-based phones. Unfortunately for WhatsApp, it does not offer this feature yet but there are some rumors out there that say that it’s working on implementing it.