Masked Moon Sect is the most powerful.
Spirit Beast Mountain is a close second.
The rest have power levels that are roughly evenly matched.
War against the 6 Devil Dao Sects
While the Treasure Seizing Assembly in the Yan Clan was happening, the Seven Sects of the State of Yue heard news about invasion of the Six Devil Dao Sects. In the following days, clans of all sizes in the State of Yue received a conscription order sealed by a Sect Master of the Seven Great Sects. At the same time, they sent diplomats to States of Yuanwu and Zi Jin for reinforcements.
Seven Sect cultivators had succesful ambush on large force of the Devil Dao, which suffered a great loss, even losing two Core Formation cultivators. Then the Six Devil Dao Sects flew into a rage and began their large-scale assault. Among the common border shared by the State of Yue and the States of Jiang and Che Ji, over ten great battles had occurred there, resulting in the deaths of over ten thousand cultivators. The Seven Sects struggled with defence. After allied forces from States of Yuanwu and Zi Jin arrived, invasion was resisted. The war sunk into a deadlock and became a battle of attrition. As a result, large decisive battles became less frequent while smaller scale surprise attacks more frequent.
After a betrayal of Spirit Beast Mountain, the Six Devil Dao Sects had great victory and the Six Sects of the State of Yue and allies from two other coutries suffered great losses. The State of Yue was in great turmoil. Despite that, some cultivators of the Six Sects, including Core Formation experts, survived and were still fighting, impeding with the Devil Dao's takeover of the State of Yue.
Remains of the Six Sects of the State of Yue took refuge with the Nine Nations Union. They settled down in the country with the least other sects, the State of Beiliang. They had to contend with the local sects for scarce resources. They also were forced to battle Moulan Tribe's Spell Soldiers.