To somehow compare the CSA Army as the greatest of all time identifies an absolute ignorance of military history outside of North America. How doe Lee and the ANV compare against Scipio, Caesar, Vespasian, Titus of Rome or a Subadai, Ghenghis, Jebe of the Mongol Empire... they don't hold a candle to them. In every single case I have mentioned those generals were not only outnumbered but grossly outnumbered by their foe, working in enemy territory and doing so for long periods of time. So compared to the ancients Lee and the ANV look like a batch of amatuers and they were, how does one compare amatuers to professionals? By their victories and the odds stacked against them... once again Lee and his ANV come up short.
The ANV was never much more than 100 miles from it's base of operations... the armies of antiquity were normally hundreds & in some cases thousands of miles away and under most circumstances dealing w/ far harsher climates and enemies who weren't real interested in taking prisoners.
To look at discipline and desertions... by 1864 desertion was a serious problem for Lee and the entire CS military. Compare that to the Mongol Army of the 1240's... desertion yeah, no.
Looking to numbers in comparisson to accomplishments... Lee & the ANV held off the US Army for 3 years; he did so with some supply issues and while being outnumbered 1.5-2 to 1. Subadai won every engagement he fought for 60 years and on almost no occasions did he ever actually outnumber his foe... and his Tumans ranged from the Korean Penninsula to the Danube. What is to compare there, really?
To put things in a perspective of the 19th century how about Lee vs a more "modern" general & army; say Wellington, Napolean... There is no need to look very hard there either. Napolean fought battles from Spain to Moscow, in some cases he was outnumbered and in some he wasn't. His win-loss record was nothing to sneeze at. Then there is Wellington... he fought from India to the channel. Sorry but when comparing Lee to Napolean or Wellington there is no comparison.
Ok how about those that came after in the 20th? Even if you take the technology out of it the US Army pushed through fortress Europe from Normandy to Berlin in less than a year against what many claim to have been the best Army & General staff in the 20th century.
So what does that make Lee & his ANV? An army that did rather well on their home turf but when it came time to fight in enemy territory... not so much. To see a more wide ranging Army of the ACW both of the AoT's need to be looked at. The US AoT had units that marched from St Paul to Fargo then to DC via Mississippi, Georgia, SC, NC, Virginia... the AoT CS had a losing record almost from the start being plagued w/ the likes of Bragg and Hood but they kept showing up to put on a good show regardless of the odds and regardless of knowing they were viewed as the red headed step child by the politicos & staybehinders who claimed their service as their own.
But to be honest NO American, or European army for that matter, holds a candle to the professional winners of antiquity. The Roman army was typically more disciplined, better trained and better led than any American or European Army of the 19th Century ( & I include those of Napolean & Wellington in that analysis) as they counquered and maintained an Empire that would set the bar. Since the time of Rome few armies have been able to compare to the Roman Legions and IMO only one has wholly surpassed them. The Mongol armies that would ravage the world from the Pacific to the Baltic & the arctic circle to the Indian ocean.
But to understand that one has to understand there is more to the world than Europe, America and the chair they're sitting in.