WhatsApp has gone over one billion users and Telegram claims to have over 350,000 people a day signing up for its services. Telegram allows you to choose whether you want a secret chat or not. Group chats of Telegram do not have encryption. WhatsApp demands access to your address book and there is no similar demand for such access. In terms of features and flexibility, Telegram is the number one option, though, WhatsApp is definitely the winner. The apps of Telegram are all open source and this means that you can modify them, according to your needs.”]
Source: https://securityaffairs.co/wordpress/49048/security/whatsapp-vs-telegram.html