If you want your source of truth to be a system outside of HubSpot, which HubSpot data representation tool is the best option?

In the HubSpot Data Integration certification, UI extensions are the best option when an external system serves as the source of truth because they allow developers to fetch and display data from that external system directly within the HubSpot CRM interface in real time. Unlike custom properties, which store a static copy of data that can quickly become out of sync, UI extensions enable a "view-only" or "fetch-on-demand" approach where users can interact with external data—such as live shipment tracking or billing history—without actually migrating that data into HubSpot's database. This ensures that the information seen by the user is always accurate to the external master record while providing a seamless experience for the sales or service teams within the HubSpot UI.