The best strategy to delete the day’s test data in a partial copy sandbox every night is to execute a batch job that deletes all records created on the day. This way, you can automate the process of cleaning up the test data and avoid manual work. Manually deleting all records individually is time-consuming and error-prone. Creating a new developer copy sandbox every night is unnecessary and wasteful, as developer copy sandboxes have limited storage and functionality. Refreshing the sandbox every night is also not feasible, as partial copy sandboxes have a refresh interval of 5 days.