Which Google Workspace application allows for easy customization of user experience through add-ons?

The correct choice is Google Docs because it has robust support for add-ons, which enhance its functionality and allow users to tailor their documents to better fit their specific needs. Add-ons in Google Docs can provide additional features such as advanced formatting tools, citation generators, and integration with third-party services, all of which contribute to a more personalized and productive user experience.

In contrast, while other applications like Gmail and Google Sheets also have some functionality for add-ons, they may not provide the same level of customization or the extensive library of tools as Google Docs. Google Hangouts, primarily a communication tool, focuses more on collaboration rather than customization through add-ons. Therefore, Google Docs stands out as the application specifically designed to allow users to customize their writing and document management through various additional functionalities offered by these add-ons.