What is the difference between a spring return, non-spring return, and electronic fail-safe actuator? What are the advantages and applications for each?

Spring Return actuators utilize an internal spring that drives the actuator open or closed on loss of power. Electronic Fail-safe actuators utilize super capacitors that discharge stored energy to the motor and the actuator is driven open or closed on a loss of power. Non-Spring return actuators stay in their current position on loss of power.