I used to use whatsapp a lot.
I'm now moving to Telegram (and probably ICQ too).
The ability to use Telegram on multiple devices and only having it tied to having the ability to receive an SMS, rather than an SMS on the single device you want to use it on is a major advantage. (e.g. personal Telegram on work phone, separating work and personal comms, on one device.)
The reason I started to move was their plan to drop support for old phones. (Half the people I used it for will be cut off.)
However the new privacy agreement has made me remove it from my phone, and put it on my old BlackBerry (until the end of the year), which has minimal contacts in the address book, and I didn't allow the app access to the contacts. This is just to catch any messages.