I have always enjoyed using Wickr Messenger for private online interactions. I enjoy the user friendly registration process that doesn't take much longer than 2-3 minutes.
You can link up to 3 phone numbers and 3 email addresses to enable yourself to quickly connect with your other friends already using the app.
The private keys are encrypted so even in the case of a MitM attack messages can not be recovered.
RT has a good video interview with Wickr CEO Nick Sell, whose eyes have never been on the internet.