Hands down the Muslim army.
The army who crushed the Romans and put the Persians in fear. The army who destroyed the Visigoths. The first army that was morally superior when it faces its enemies. A army that defeated its oppenents despite all odds. Khalid Ibn Waleed (military genius) and 3000 Muslims defeated 100,000 Romans (army of Roman governor Ghassani ).
Heraclius who was at the height of his glory by defeatin' the Persians in an encounter was awe-struck when he heard the defeat. If 3000 Muslims defeated 100,000 Romans, then 30,000 Muslims who were waiting for him would not be so easy to defeat.
Muslim army (mostly infantry) defeated the Visigoth army of Roderick (30,000 excluding the large number of Cavalry on the Wadi-laqqa).
Defeated the Persians 2 times (again despite the odds). Up to 10,000 Muslims defeated 40,000-50,000 Persians. Three years later at the battle of Qadissiyah, Muslims defeated them again with an army consisting of 15-20,000 against 60,000 Persians.
And how can I forget Saladin who defeated the Crusaders and even earned the respect of his enemies (Crusaders). And then you got the battle against Napoleon, and so forth.
Unfortunaley, the compassion and mercy of the Muslims was their downfall. The savages (Crusaders, Moghuls) attacked and massacred the non-combatants. But they defeated the Moguls at the battle of Ain Jalut.
Dr Lebon:
"In truth, nations have never known merciful and tolerant conquerors like the Muslims."
A new Caliphate with with a new Saladin as the Caliph would no doubt keep keep these capitalists at their distance.