Hanzo's poison was deadly, causing victims to experience excruciating pain until they succumbed to numbness, where these effects would then progress to complete paralysis and ultimately death within a period of two days from inhalation.
Hanzō always breathed using a respirator and carried a small vial of antidote with himself, although even immediate ingestion of this did not guarantee survival.
Sasori's poison was so strong that even if a small amount is introduced into the bloodstream, the affected person will die within three days while also being painfully paralysed for the duration. According to Sakura, this poison is refined with heavy metals which gets into the muscles and destroys the cells.
Hanzo's is more deadlier as just a simply breathing it will get you, whereas Sasori actually has to directly hit you with it.