I am going to stick my neck out and give some of my choices, at least partly to perhaps gen up some interest. On the Confederate side for best brigade commander, although Armistead early on and at Gettysburg did fine work and Barksdale at Fredricksburg and Gettysburg did well also and Hood at Gaines Mill during the Seven Days was a dynamic leader, I have to go with Jackson for his work at First Manassas. For best division commander, one has to consider Powell Hill, especially at Sharpsburg and John Gordon at Sharpsburg also but my choice would have to be John Bell Hood for his work at Second Manassas, Sharpsburg, Gettysburg and Chickamauga. When he became an Army commander he did not do well, perhaps because of poor health but as a division commander he was all lion. As a corps commander I am tempted by the commander of the First Corps, Army of Northern Virginia, Old Pete. However, for the Shenandoah campaign where he actually commanded a small army and for Second Manassas where he commanded a wing and at Chancellorsville, I have to go with Stonewall Jackson. Incidentally, in the 40s I attended a brand new grade school in Dallas called Stonewall Jackson and his black bearded visage graced the entrance of the cafeteria so I saw him everyday.
Now, in reverse order, for the best corps, I am going with the First Corps, Army of Northern Virginia, commanded by James Longstreet, Old Pete. Once Jackson was gone Lee relied on the First Corps more and more because his other Corps commanders had not the quality of Longstreet. That corps with the divisions of McLaws, Pickett and Hood was a formidable fighting force. For the best division I pick Hood's Division for the work at Second Mannasas, Sharpsburg, Gettysburg and Chickamauga. In the evening after Sharpsburg, where Hood's small division had smashed the Union attack at the Cornfield and the Dunker Church in the morning of that terrible day, Lee asked Hood where his division was and Hood replied that they were there lying on the field. Some of his regiments took casualties of more than 80 % that day.
Which leads me to my pick for the best brigade for the South. The Stonewall Brigade is obvious for First Manassas and almost every other major battle in the east but I am going(surprise) with The Texas Brigade also known as Hood's Texas Brigade. They reached the east too late for First Manassas but stayed busy from then on. There were three Texas regiments, the 1st, 4th and 5th Texas and in the beginning they were augmented with Hampton's Legion and the 18th Georgia, the Goober Grabbers. Later the Brigade lost the Legion and the Goober boys and were joined by the 3rd Arkansas, a big regiment, for the rest of the war. They first fought at Eltham's Landing during the Peninsular Campaign but first made their name at Gaines Mill under Hood during the Seven Days when they broke the Union lines along the Chickahominy. Hood went on to command a division after that which the Texas Brigade was part of and they played a major role at Second Mannassas, Sharpsburg, Gettysburg, Chickamauga, East Tennesee, The Wilderness, and all the rest of the campaigns leading up to the retreat from Richmond where the remnants of the Texas Brigade served as the rear guard for the Army. The three Texas regiments enlisted 4000 men during the war and 1000 died and most of the rest were wounded, some multiple times. An oddity was that on both sides, North and South, the ratio of deaths from disease versus battle wounds was about two to one. In the Texas Brigade that ratio was reversed, twice as many died in battle as from disease. Lee said of the Texas Brigade, "Their coats were ragged but it did not matter for the enemy never saw their backs."