Wellington was far better at leading an army in battle.

George Washington's genius lay in his ability to ensure that the rebels maintained an effective field army. If they had chosen to fight a major European style battle and lost, the rebellion would have collapsed. He was one of the few Americans who realised that local militia units could not be expected to routinely defeat British regulars on their own, or even turn out and fight for a loser.

Incidentally, the British led force at Waterloo slightly outnumbered the French, but the French had better artillery and the only troops that Wellington knew he could really count on were the veterans of his penninsular campaign, who suceeded in routing the Imperial Guard.