How does Telegram's encryption compare to other messaging systems?
Signal, as already said, has e2e encryption by default. Out of the major messaging apps, however, it appears to be the only one (at the time of this publication). Facebook Messenger is not automatically e2e encrypted. Like Telegram, one has to make the chat "secret."
Whatsapp, which Facebook owns, has end-to-end encryption for chats between family and friends, but the rules get murky when it comes to business chats. The app planned to change its business chat encryption in a policy update on Feb. 8, but due to backlash they pushed it to May 15.
Whatsapp messages between friends and family are end-to-end encrypted by default. However, your Whatsapp messages to businesses may not be end-to-end encrypted starting on May 15 if the business has granted access to third-party vendors, like parent company Facebook, for hosting purposes. When you start a chat with this type of business you’ll see a light blue message at the top explaining what kind of privacy you can expect. If the chat with the business is end-to-end encrypted, you’ll see a note at the top of the chat in yellow saying so.