The I2P protocol would have been a much more interesting and secure choice imho.
I'm impressed by the Tox effort, going to keep a close eye on that one, open source, multi-platform, very good initiative!
Bitmessage is great, but slow as #@$! and not available for mobile devices.
Bleep is out of the question, closed source proprietary spy junk.
Tox looks good indeed. You can add another layer by tunneling it through Tor too and maybe a future release implements it directly.
Secure messaging has to be as simple as possible because your everyday WhatsApp/Snapchat user does not want to invest time into security.