I have to second this recommendation. Telegram seems to have solved most of the issues I've seen in other cross-platform apps. One feature I really love is that conversations REALLY STAY IN SYNC. If you log into Telegram on your computer or tablet, you will see *exactly* the same view that you had on your phone, including the same conversation history.
The various clients work really well, and they don't use weird hacks like using your phone as a proxy for their desktop app. They also recently implemented two-factor authentication if you desire it.
It's a great app.
The iPad app is pretty screwed up for me though. The conversations are all not ordered according to time and it doesnt list the names of my contacts. It works fine on my Mac and iPhone though.
The problem is that people in my country default to Whatsapp. Its quite remarkable how a third party application has become so popular in some parts of the world that it has even completely replaced SMS, and ironic how its now itself the obsolete messaging service that needs replacement.
I try to use Whatsapp as little as possible as long as it does not have cross device support.