What made you decide Telegram was a worse choice than Whatsapp? At least Telegram doesn't send nasty letters to people developing unofficial clients.
As the saying goes: "don't roll your own crypto, unless you're a professional cryptographer, and even then…". Telegram are not cryptographers but decided to roll their own anyway and have come in for not a little flack as a result.
Search for "telegram app crypto criticism" and you'll find plenty of examples of this.
Is Telegram secure? I'm not qualified to answer that, but I understand enough to be sceptical.