Washington and his Continentals were a vastly different type of opponent than Napoleons Grande Armée. Wellingtons success against the latter really isn't a good indicator at how he'd fare against the former. Conversely while Washington prevailed against the succession of competing British Generals things might have turned out different against a general of Wellingtons stature.
This illustrates a problem I have with designating best of anything but especially military leaders. Success in war is far too dependent on a multitude of factors that are out of the leaders control.
Take the Battle of Trenton for example. Had the Hessian pickets been a little more alert that chilly morning, or had Col Raul bothered to read the message in his pocket delivered the night before that detailed Washingtons plans the battle could have been a disaster for the Continental army.
What we call an example of the military genius of Washington we might well see as a prime example of his incompetence.