Telegram's clients are amazing (including the ones developed by the community, such as telega.el for Emacs). It is miles ahead of any other messenger in the UX department. Friends of mine who have (reluctantly, in some cases) tried it out quickly got stuck because of this single point.
The other thing it's got going for it is that its protocol is designed to work in low-bandwidth environments. Yeah, the protocol looks crazy - but it really does work. Imagine being on an underground train and only occasionally getting a few seconds of internet while passing a stop: Most messengers will at most start showing you a "Connecting ..." status, Telegram will do a full state sync (minus media files, of course) in the same time.
The other thing it's got going for it is that its protocol is designed to work in low-bandwidth environments. Yeah, the protocol looks crazy - but it really does work. Imagine being on an underground train and only occasionally getting a few seconds of internet while passing a stop: Most messengers will at most start showing you a "Connecting ..." status, Telegram will do a full state sync (minus media files, of course) in the same time.