"The difference between Lee and Grant as leaders. Battles are won by slaughter and maneuver. The greater the general, the more he contributes in maneuver, the less he demands in slaughter."  Winston Churchill

In my opinion there is no comparison...Had the two fools Pillow and Floyd not surrendered Ft. Donelson after our boys soundly whipped Grant, he would have been run out of the Army.  Classic case of saving defeat from the jaws of victory; no one was more surprised than Grant when surrender was offered by the two incompetents...Halleck and McCellen hated Grant and considered him a worthless drunk.  Donelson was a crucial turning point in the war and it's loss is grossly under reported in history.  

Next Grant is practically driven into the Tennessee River at Shiloh on the first day, only to be rescued in the middle of the night by the arrival of Don Carlos Buell's 24,000 reinforcements.    

At Cold Harbor Grant lost 7,000 men in half an hour and still called for more attacks but, his subordinates refused to obey.    In the Overland Campaign of 64' Grant had more casualties than Lee had in his entire army.  Heaven only knows what might have been had our boys been able to get some food; men can't fight on nothing forever.

The only thing Grant had over Lee was overwhelming superiority in numbers of men and material.  I stand with Churchill on this one...