Categories or Structures: Most efficient way to organize FAQ sections
If your clients wants to have control about the order of the entries for each audience,  e.g. 

 Trainee
 Advertising
    Ad Entry 2
    Ad Entry 3

 Associate
 Advertising
    Ad Entry 3
    Ad Entry 1
    Ad Entry 2


a good solution might be a entries field. The ability to simply drag and drop entries to change the order is the most intuitive option from my experience. If you have many entries you could combine both logics - e.g. render first all elements that you selected with the entries field and after that add the missing ones according to your categories / structure.