The answer to this question is that one really cannot tell. This is no slight to many of the great generals and admirals that have served, but due to a fundamental truth. Warfare is constantly evolving. The basic infantry weapon has evolved from the spear to the sword to the gun. The gun evolved, as well - the musket was replaced by the rifle, which ultimately emerged as the assault rifles of today. Horses were introduced, then eventually replaced by various vehicles, including the tank. Artillery has evolved from catapults to trebuchets to cannons.
Even the evolution has evolved as well - for instance, today's artillery is far more accurate due to technology like GPS, and the shells fired have become more complex and deadlier. New technologies have evolved as well. Air power has emerged - and has evolved from rickety biplanes to jets that can fly twice the speed of sound. Attack helicopters have emerged as a viable means of close support as well. A far cry from using horses to get somewhere fast.
These evolutions have changed the tactics that would be advisable. Prior to 1865, soldiers would bunch up - often to protect each other. With the advent of machine guns and widespread equipping of infantry with rifles, bunching up was a very bad idea. And so new capabilities emerged, with new tactics designed to take advantage of these capabilities. New strategies had to be employed to deal with those tactics. Many of these new strategies are things that are second nature to a general like Tommy Franks (who commanded the liberation of Afghanistan in 2001 and Iraq in 2003), but would not have entered the minds of Napoleon and Wellington.
Comparing Hannibal's performance in the Second Punic War (218 BC to 202 BC) to that of the Duke of Wellingtonin 1815 is like comparing apples and oranges. Such a disparity is often best displayed by the Italian invasion of Ethiopia in 1935 - many of the Ethiopian troops were armed with spears and bows - state of the art in Hannibal's time, but woefully out of date in 1935. Hannibal's genius would matter little if he faced mustard gas, machine guns, and airplanes. Much as the case with fighter pilots, the best approach is to often limit the comparisons to various eras, when one can assess the generals and strategists on a level playing field. - Harold C. Hutchison (firstname.lastname@example.org)
Who was the best strategist of all time? This is a question that draws hours of debate, and very few minds get changed. Was it Hannibal, who defeated the Romans at virtually every turn? Was it Erwin Rommel, the famed Desert Fox? Was it Robert E. Lee, who held off vastly superior forces during the Civil War, or U.S. Grant, who defeated him? Was it George Washington, who successfully kept the American cause alive from 1775 to independence in 1781? Or was the best strategist someone like Alfred Thayer Mahan, who wrote "The Influence of Sea Power on History"?