I wonder which of these the intelligence services prefer. Every one of them has their own advantages and drawbacks in terms of predictability, reliability, long term stability and chances of double dipping/playing both sides.
Most of these assets are not super spies. They have access to one particular type of information and the adversary squeezes all they can until all the juice is gone. Sophisticated espionage and double agents only exist in le Carre novels now.
