If not for the increase in gas price, I would normally use clay pot to boil soup. Soup boils in clay pot help to preserve the taste and flavor. The pot has high heat resistance and can cook over medium-low heat for a long period of time. They have good aeration but low heat radiation, therefore suitable for cooking long-boiled soup.
To preserve the life-span of the pot :
Soak the new pot in rice water (rinsing water) for 1-2 days to let the water blocks any small cracks or holes at the surface of the pot; or
Oil the outside of the pot and fill pot with warm water. Leave it overnight and bring to boil over low heat. Cool and pour away water and pot is ready for use. This is to prevent pot from cracking easily.