Reference

Regarding the references, it is better to give the people who hold the higher position/famous in that area or it is ok just to ask coworkers as the reference. For example, I worked with the one who was the company’s VP but has moved to other company as CTO. I can ask him as my reference but I don’t know if it is worth to bother him since he is busy.
I received the call from hiring company asking the relationship about the references I provided (they are my coworker/previous coworker/professor from school) with me.