Actually IMO the Army of the Potomac was the best behaved union Army. Not saying much though. They were good at marching south and running north.
And yet at the end of the war, they were the ones having a victory parade.
They would have run away once and the whole matter resolved quickly, were it not for that darned McClellan fellow.
After the War Lee also never allowed an Unkind word to be said about Grant in his Presences.
For his Magnanimous attitude, because Lee knew, that as the Vanquished, if it were any other country on Earth Grant would have been in his rights to have taken Lee back behind a Tree at Appomattox and had him Shot as a Traitor.
But he didn't.
It also marched West to Appomattox.