Fail-safe rotary solenoid, linear solenoid or stepper motor.

Which option would be the best for the quickest response time, torque and lowest price.
Continuous duty rotary solenoids are said to have higher starting torque, and might achieve faster response time when attached to central axis of the drop flap, compared to crank arm mechanism required for linear solenoids, but they appear to be overpriced.
Not sure if stepper motors are fail-safe enough for this application.
Pneumatic actuators are not practical enough in this case.
Thank you.