Which Spirits were most important to the ancient Chinese

Their own family ancestors

Explanation:

Ancient chinese believed that their dead ancestors lived in the afterworld, and those spirits had magical powers. Moreover, the spirits were looking after you all the time, and they may take care of you or hurt you depending on how you honored them. In all the houses, there was a shrine used to honor the dead ancients; they would bring food and drinks to the shrine in order to celebrate the spirits.

Their own relatives meaning ancestors