Telegram is scary and questionable. Inventing your own encryption is never the answer and reeks of horrible understanding of security, at this stage there is no reason they should not adopt a standard of communication like Signal protocol. Signal app itself is ok, it's a little....annoying as it requires a phone number and the UX needs some love. Keybase is great, It has ways of verifying you across multiple services…
We still haven't seen any examples of Telegram being compromised.
Closed source (both in code and implementation) has no place in the security world and anything security related should always be open for anyone to scrutinize.