Tried Whatsapp once, hated it, never tried again. Viber is even worse.
Telegram has been what an IM program should be, for years now (it gave me the vibe of my much beloved Miranda IM almost 20 years ago). I'd love it if they added more link previews (9GAG and Instagram previews stopped working almost a year ago and the functionality was never recovered) and even more keyboard shortcuts for full navigation without a mouse -- but even without these it's the most solid IM experience I ever had.
Maybe they are not as encrypted or protected in general as Signal. Maybe (but what do we know about Signal, save for a lot of claims?). But the fact that several governments and corporations demanded them to give access to various keys or to shut down channels is a testament that Telegram isn't as amateur in encryption and protection as the overly nitpicky HN audience would have you believe.