Help on epq question

I am doing an extended project qualification with my school. I have four question ideas and need a bit of help deciding which one is the best. They are:
What factors ended the viking raiding period?
Was Napoleon a tyrant or a hero?
What lasting effects have the crusades has on modern western-muslim relations?
What was the real purpose of stone circles?
They are only basic question ideas and can be adapted but i need some help deciding which would be the most appropriate to research.