Grant was the greatest general of the war mostly because, unlike Lee, he had to overcome a massive amount of politics to fight in his way. Grant had to fight politicians as hard as he fought Lee.
Grant was the best strategic general of the war, according to R.E. Lee. I see Sherman as a close second, late in the war. I don’t see any dispute on that.
Tactical generals, I see Sheridan, Longstreet as being near peers, and one could also make a case for Jackson based on two campaigns. Sheridan was luckier. Longstreet was wounded at key moments.
Worst generals: Butler, Burnside, and Hood.