Final answer:
The best method to track additional customer information in QuickBooks is to use the 'Additional Info' tab to create a Custom Field directly in the software.
Step-by-step explanation:
The best way to track a specific piece of information about your customers that QuickBooks does not currently track is option 3: Edit a customer and click the "Additional Info" tab, then click Define Fields to create a Custom Field. This allows you to directly add and track the new information within the QuickBooks environment for each customer profile without the need for external programs or temporary solutions.
The Notes feature could be a quick way to jot down information, but it might not be as organized and analyzable as a customized field. Exporting the customer list to Excel, adding the information there, and re-importing the list could be time-consuming and prone to errors, whereas creating new fields within QuickBooks maintains data integrity and workflow efficiency.