I'll continue to use WhatsApp for another month or so, until TextSecure becomes available for iOS, after which I'll be helping everyone I know switch to it.
Not the GP, but: No open-source server as far as I can tell (i.e. "cannot host it myself") and questionable security track record at the moment. The latter is something that can be fixed in parts, but .. without the ability to _not_ send my private conversations to a random company and tie my "identity" to their service I've got to decline.
To be clear: I've never used WhatsApp either - so I'm not really supporting the 'WhatsApp > Telegram' idea.
I'll continue to use WhatsApp for another month or so, until TextSecure becomes available for iOS, after which I'll be helping everyone I know switch to it.