Custom Taxonomy or Field With Options?
How do you choose if you should use a custom taxonomy or a custom field with options?
Think about how you want to use the field. Do you want to be able to view a grid for each option? Then you should use a taxonomy.
Do you know how many options a field will have? Is it a fixed set? Then a field with options might be fine. Do you want to be able to create new options right from the book page? Then you want a taxonomy.
Do you need to be able to hide the field due to potential spoilers? Use a field with options.
Need the options listed in a certain order? Use a field with options.