The reason why I tend to go ancient is the very reason why some say to go modern. With dictatoral powers comes dictatoral responsibilities. What I mean is Lee might have been a good stategist BECAUSE he didn't have to worry about anything else, while some of the general-kings of the past not only accomplished unheard of military feats (Caesar conquered Gaul, Alexander all of known Asia, Belesarius the entire Western Roman Empire, Lee a few dozen sqauare miles of South Central PA) they also built cities, reformed laws, fought political intrigue, etc... I guess you have to include scale when discussing these sorts of things, as modern military commanders do not have a chance to do both, let alone at the same time.
-Pat