Before anyone answers this, I think it is necessary to define the role of the cavalry of the time. It was a body whose job was screen their army's movement, gather information on enemy movements, raid the enemy's lines of communication and supply depots, protect their army's lines of communication and supply trains. Thereby generally cause the enemy to keep large bodies of troops to counteract the above. John Singleton Mosby and John Hunt Morgan did not embody these attributes. Both were independent raiders rather than an Army component. Forrest , while brillant as an independent commander of what was basically mounted infantry, did not distinguish himself when acting as a componant of an army, as at Chickamauga. JEB Stuart, Joseph Wheeler, Wade Hampton, Philip Sheridan, James Wilson, Wesley Merritt and a few others were commanders of the Cavalry componant of larger armies, and so are the candidates I would choose from as they performed all of the duties outlined above. IMO, Stuart was the outstanding performer. His screening of the ANV up to the Potomac at the start of the Gettysburg campaign was masterful, and his protecting the army on its retreat was brillant. At Chancellorsville, his troops found the AoP right flank open to attack and presented the opportunity to Lee. The long scout around the AoP in 1862 found an isolated componant of the AoP, and his intelligence gathering formed the basis of the Seven Days campaign. Wheeler was under-supplied and trying to operate under very difficult geographical condition while out-numbered by an aggressive, well supplied enemy. Hampton came into his own late in the war but proved himself as an intelligent leader who possessed the knack to "read" a situation with perfection. Sheridan was not a team player. Sheridan's June 1864 horseback ride took away enough of Lee's reconaissance ability to mask Grant's crossing of the James River. This would fall under the cavalry's duty to screen the army's movements. However, this was an intended benefit of a largely failed ride. The ride lost a great opportunity for the Federals. His aggressive style paid off in his unrelenting pursuit of the retreating ANV in April, 1865, may have prevented the ANV from joining with Johnston's Army, therby prolongimg the war. He certainly wore the fight out of the ANV. Wilson and Merritt were by the book soldier's who did just about everything right but did not have the stage to work with as did the others.