WhatsApp and Signal both feature end-to-end encrypted chats by default, implying that anyone with access to their serves cannot read your chats. In Telegram, you can keeps your chats personal by enabling the ‘secret chat feature’. The reason why Telegram does not offer end-to-end encryption by default is because the absence allows a user can send large videos and documents using Telegram.
None of the three apps display advertisements. Telegram has announced plans to introduce ads to its platforms to keep it running independently, though they will be restricted to large one-to-many channels only, Durov has said, as reported by Indian Express.
All the three apps offer the screen lock feature, which enables a user to put a lock over their private chats, much like how you put a lock on your phone. Screen Lock feature allows a user to leave his phone unlocked and unattended without having to worry about his private chats
All the three apps offer the disappearing messages feature, though in Telegram you can use it only in the ‘secret chat’ mode.
Group chat security
WhatsApp and Signal both feature end-to-end encryption on group chats. In Telegram, you can keeps your chats personal by enabling the ‘secret chat feature’.
WhatsApp backs up your chat on third-party cloud platforms, while Telegram has its in-built cloud back-up. Signal does not offer chat backup option and they are saved on your device itself.