What is the MOST operationally efficient solution that meets these requirements?

Explanations:

While creating a Lambda function to automate the creation of CloudTrail trails could work, invoking it daily adds unnecessary complexity and operational overhead. It would not efficiently manage new accounts as they are created, requiring continual updates to the Lambda function or handling state management.

Creating a CloudTrail trail in the management account that logs events for all AWS accounts in the organization is the most operationally efficient solution. This allows centralized management and monitoring of all accounts without needing to create and manage individual trails, ensuring all events are captured across the organization efficiently.

While creating a trail in each account and preventing deletion or modification is a robust security measure, it requires ongoing management as new accounts are added, which increases operational overhead. This approach does not leverage centralized logging efficiently.

Using a Systems Manager Automation runbook is a valid approach but adds complexity and overhead compared to directly managing trails from the management account. Like option A, it requires running the automation whenever a new account is added, leading to more operational effort without significant benefits over option B.