Anyone who thinks that one brake, front or rear, applied by itself is more effective than both applied together is forgetting one very important fact, tire contact with the pavement. It is the force applied through the tire to the ground/pavement that determines what happens to the cycle's direction. It is the magnitude of that force that determines how fast the desired event occurs. For maximum braking one must use all the square inches of tire/pavement contact. If one only uses one brake only the area of that tire's tire/pavement contact is used while the other is ignored; hardly a formula for maximum braking.

So, for maximum braking use both brakes maximally while shifting rider weight as necessary to maintain control. For modulated braking use whatever the rider is comfortable with; after all only partial braking is needed under that circumstance.