The correct answer is - The Byzantine Emperor was the highest political and religious figure. In the West Empire, the highest political and religious figures were two different people.
In the Byzantine Empire, the emperor had a complete authority, both over the politics of the empire, and the religious activities and politics in it. He was the highest figure with absolute power in every segment of the empire.
In the Western Empire, the roles and authorities were divided between the emperor and the pope. While the emperor was in charge of the politics of the empire and had the authority in that aspect, the pope was the one that was controlling the activities and politics of the Church. The amount of power they had individually was pretty much on the same level.