The Law of Conservation of Energy simply stated is that energy cannot be created or destroyed, but can change from one form to another.
Think of Potential Energy as the amount of 'work' that could possibly be done and Kinetic Energy as using that Potential Energy in the performance of 'work'.
The goal of establishing the most possible Potential Energy is in finding or developing the best stance in the batter's box.
Potential Energy - The raising of the bat and the stretching of the muscles that will bring the bat down and forward is done by flexing the opposing muscles to the muscles we wish to contract in the swing. This position has established some degree of potential energy to be used in the swing.
Kinetic Energy - Stride/weight shift in conjunction with swing launch to a contact point directly over the center of the plate begins the developement of bat speed to the point of desired contact.
When stride/weight shift ends, the upper body and the bat speed up if the bat path is circular.
The effective thrust of hip turn in conjunction with the already established circular motion of the bat further increases bat speed.
Since the initial thrust of the bat to extension, using gravitational and muscular propulsion, causes the primary forward momentum of the bat, I choose to call this method a 'top down approach'.
Thus it would be gravity plus arms, aided by the stride/weight shift ending and the additional thrust of hip turn offer the greatest propulsion of the bat head with the least amount of time and energy used in the accomplishment of the task.
In reality, the 'best' swing style will always be the one that garners the best results for a particular batter.