Question

did any one person or class hold the most power during the middle ages, or did it shift back and forth

Answer 1

The royals and nobles held the most power.

Answer 2

During the middle ages, the nobles or royalty held most of the power while also sharing a good part of it with the church. The church was followed by everyone while the royalty had limited control over the church. In a way it shifted back and forth but it was mainly in the hands of one ruler.