The Electronic Frontier Foundation has released an interesting comparison chart showing how well the most common instant messaging platforms compete on security.

The EFF analysis looked at these criteria:

• Encrypted in transit
• Encrypted so the provider can't read it
• Can you verify contacts identity
• Are past communication protected if keys are stolen 
• Is the code open to independent review
• Is security design properly documented
• Has the code been audited
  Are

The highest rated tools (scoring 7 out of 7) were:

• ChatSecure
• CryptoCat
• Signal/Redphone
• Silent Phone
• Silent Text
• TextSecure

Not surprisingly, Apple's Facetime & iMessage (Messages) were ranked as the most secure mass market messaging tools. 

Google Hangouts, Facebook Messenger, Blackberry Messenger and Microsoft's Skype were dinged on several fronts including lack of protection of past communications and lack of detailed documentation about security.

EFF Press Release : Link

EFF Scorecard : Link