I super appreciate what Telegram is trying to be as far as messaging apps are concerned. They're doing their best to deliver a fast and secure messaging alternative that isn't necessarily controlled by the big companies. WhatsApp offers similar encryption for chats but it's also now owned by Facebook and they're well on their way towards fully monetizing the platform. Google Hangouts is pretty reliable but it has always been a little niche as people never quite warmed up to Google Talk integrated into Gmail.
Realistically most of my chatting happens on Google Hangouts and Facebook Messenger due to sheer convenience. Hangouts is where Tobie and I talk the most while Facebook Messenger is the easiest way to reach the most friends, especially when it comes to the complicated world of game scheduling. And then locally Viber is still the predominant SMS alternative for people who prefer to rely on data instead of SMS. WhatsApp is mainly a work thing, especially when it comes to coordinating with Singaporean clients.
It's subtle, but I will concede Telegram is a pretty good product in terms of it being faster (you'll notice it over time) and still more reliable than the likes of Viber. But you go where most of your contacts are and it's hard to get people to switch away from where their contacts are, so on and so forth. And so my default continues to be Facebook Messenger for that wider reach and Viber for easy association with mobile numbers.