(From the military history of Esposito and Elting.)

Davout:

Of all the marshals, Davout had the strongest character. He was obeyed by his subordinates---even Vandamme---but was respected rather than loved. medium height, robust, severe features, prematurely bald. Very near-sighted, he wore special combat glasses that fastened at the back of his head. Cold, methodical, incorruptible, quiet, with an agile and open mind. An expert organiser; supervised the creation of the Duchy of Warsaw. His troops were always the best trained, equipped, and disciplined in the Grande Armee, and usually got the hardest assignments. Strict with his officers, he remembered and rewarded competence, and took responsibility for their mishaps when they had acted according to his orders. Had unusual skill in intelligence work. Although he was harsh in his dealings with civilians when it was necessary to feed his troops, he permitted no looting. Excellent tactician and strategist; never defeated. Soldiers called him "The Just."
Barclay:

A soldier of character: "calm, cool, possessed of a sense of order and discipline, and of great endurance." A stout fighter, able to keep his head in a crisis. Moderately good tactician; no real strategic sense. Had, as Russian command went, considerable administrative ability. Could resist tremendous personal pressure and abuse. Not popular with his officers and men. (According to some accounts, Barclay never really mastered the Russian language.)