Explanation: For Cloud Kicks' requirement to refresh an audience daily for an upcoming journey using a data filter in Automation Studio, the most suitable entry source for the journey would be a Data Extension. Data Extensions in Salesforce Marketing Cloud are powerful tools for managing and storing customer data. They can be easily integrated with Automation Studio, where a data filter can be applied to refresh the audience data on a daily basis.

By using a Data Extension as the entry source, the marketing team can ensure that the audience for their journey is dynamically updated based on the criteria set in the data filter. This ensures that the journey is always targeting the most relevant and up-to-date audience segment, thereby increasing the effectiveness of the marketing efforts.

References: Salesforce Marketing Cloud's documentation on Journey Builder and Automation Studio provides detailed insights on how to leverage Data Extensions as entry sources for journeys and how to utilize data filters in Automation Studio to dynamically update these audiences.