rigidbody.velocity vs lerp efficiency

I have two ways of moving objects:

Method 1

 void Update(){
     rigidbody.velocity = ( targetPosition - transform.position )*speed;
 }

Method 2

 void Update(){
     transform.position = Vector3.lerp( transform.position, targetPosition, Time.delta*speed);
 }

Which one is more efficient? Does rigidbody.velocity use the GPU?