For me, Instant Messaging became a thing in Czech Republic with the appearance of ICQ. A horrible piece of proprietary crap, but hey, you could send people messages over the internet for free!!!1!!1one
So I tried using xmpp/jabber instead for a long time and I had a few contacts I cared about on it and with Google Talk supporting it, xmpp looked like it might become the open standard we deserved.
Well, nope. Google dropped xmpp support, supposedly because it didn't meet requirements of the new age. Well, that didn't help them I reckon because Hangouts are unreliable piece of crap, sometimes delivering messages with tens of minutes of lag or not at all. They didn't even get notifications on multiple devices right... The poor quality of Google's parody of IM service already caused me distress in real life.
Disgusted, I also gave Facebook Messanger a try as I met some people who are best reachable through it. I must say it works very well for me, order of magnitude better than Hangouts. Messages are delivered quickly most of the time and you can see if a message reached Facebook servers or even arrived at some of recipient devices. Oh, and you only get one notification when you sit on your PC with Facebook open and phone in your pocket. I like the Messanger but I have the privacy and security concerncs with Facebook.
Finally, there's Telegram. Although the servers are proprietary, it's backed by non-profit organisation and open API and open source clients are available. The service is bound to phone nubmers, so no need to exchange contacts again and registration is trivial with accounts automatically destructing over time. Most importantly, this service seems to be secure by default and providing end-to-end encryption. Read their FAQ and join me in the testing if you please.