Perhaps an appropriate converse question to ask here could be, 'Which senior General was the most humble or displayed the greatest humility?'. In other words, 'Was there any General 'who left their ego at the door, when they entered a room'. Agree, it would be a much shorter list.
In my view, Ambrose Burnside might take the prize in this category. Thought Burnside was a rather unassuming and modest person, who knew his own limitations, but who got unwillingly promoted to high command positions. Thought, though, that these personal traits might have been significant factors in his failures in both business and the military.
Following the debacle at Fredericksburg thought Burnside felt the full weight of the defeat and fully absorbed all of the blame, without excuse. He would ultimately offer his resignation of Army command which Lincoln accepted. During this period, Burnside declared, …"It is the duty of every public man who found himself an impediment to the accomplishment of the greatest amount of public good, to give way to some other person who possessed the public confidence."… These expressed sentiments by a modest individual were in marked contrast to the egotistical McClelland's reaction in similar circumstances (when facing imminent dismissal from high command). The modest Burnside would again admit his shortcomings in mid-1863 by saying, …"My Fredericksburg campaign failed and I assumed responsibility for the failure."…
Thought the comparison with Burnside's behavior in high command serves to highlight the extent of McClellan's egotism.