WhatsApp by default backs up to Google drive, which is laughably insecure.

I don’t know how good is WhatsApp’s e2e implementation, I’ve heard good things about protocol though. But I do know Telegram protocol documentation contains all information needed to implement e2e capable Telegram client, and their e2e is really good, I’ve seen it done by my friend and as I’m a programmer and am interested in cryptography, I followed his work very closely.

I still do not trust e2e group chats, it’s a shaky point in security protocols. There was some kerfuffle about WhatsApp being able to silently add invisible listeners to group chats, wasn’t there?

Telegram very explicitly chooses the right amount of security and makes user aware of inconveniences this level of security brings along. WhatsApp lies in user’s face, making you think it’s secure and convenient.