Telegram is a farce. They don't have end-to-end encryption by default, and their encryption protocol(MTProto) is home-made and basically a secret. They haven't opened it up to testing or open sourced it, so it's pretty useless at ensuring 'privacy'. Plus recently 15 million phone numbers linked to Telegram accounts were hacked because of an SMS verification loophole.

WhatsApp at least has end to end encryption- though that alone isn't enough, but it is not open source and is owned by Facebook. By default, it shares your number and your contacts' numbers with Facebook.

Neither Telegram nor WhatsApp are viable alternatives to anyone interested in privacy.