George Washington, then U.S. Grant. Washington accomplished more with less than just about any general in history against the global superpower of the day. Grant won every battle and accomplished every strategic objective, whether outnumbered or not. He understood how technology was changing modern warfare and adapted. As for the south, I think Longstreet was their best general. He was cut from the same cloth as Grant, IMHO.
Lee failed twice to invade the north, and ultimately lost. As for MacArthur he was methodical, but made two colossal errors that cost the lives of many troops. First he allowed the Air Force to be destroyed lined up on the ground at Clark Field eight hours after Pearl Harbor. Second he ignored the overwhelming evidence that China had infiltrated a half million troops into North Korea including captured Chinese soldiers, because he held the Chinese in contempt as soldiers. He also allowed them to not build proper defensive positions in case they needed to retreat, unlike the Marines who build firebases along the way. The result was the destruction of his 10th Corps (that he named after Ceasar’s 10th legion). Those two blunders bring him down though he was still a great general.
And related by marriage. Grant's wife was Longstreet's cousin.
Being reluctant to send an army into someone else's country may have nothing at all to do with being unaware of it's military advantages. For Lee it may have been a moral conundrum in which he sought to avoid hurting people for which he had no malice.
Had he been more of an unethical cold hearted bastard, he might have done what was militarily advantageous instead of what he believed to be the proper moral thing.