Hi Vicky,
I don't know if there's any established best practice, but logic suggests that you configure and store the values in one of the Customer Group fields - either the main "Customer Group" on the "Sales" tab, if not already in use, or one of the 5 fields on the "Additional Data" sub-screen.
My feeling is that you'd want the information at Sales Area level, in case a single customer had different roles in different areas. For example, one of your customers could directly consume your products in one Sales Area, but act as a reseller in another. If you were sure that could never happen, then there would be potentially less maintenance by using a General level field - for example, the "Customer Class" field on the "Marketing" tab.
Does that chime with your own thinking?
Regards,
Dave