I would suggest that the worst were:
The Pindaris: These were were irregular military plunderers and foragers in 17th- through early 19th-century India who accompanied initially the Mughal army, later the Maratha army, and finally on their own before being eliminated in 1817-18 Pindari War.
As irregulars, they were not paid and made their living by plunder. Their atrocities were so severe that even the armies they followed had to rigidly control their activities.
There were an estimated 20,000 to 30,000 Pindari militia around 1800-1815 AD who looted villages, captured people to sell as slaves and challenges the rule of the local Sultans, Kingdoms, and colonies. 1795 to 1804 came to be called the “Gardi-ka-wakt” (“period of unrest”) in north-central India.
Such was their depravities that villagers would kill themselves and their families to avoid capture.