What is the MOST operationally efficient way to determine the Region in which the template is being deployed?
Use the AWS::Region pseudo parameter.
Require the Region as a CloudFormation parameter.
Find the Region from the AWS::StackId pseudo parameter by using the Fn::Split intrinsic function.
Dynamically import the Region by referencing the relevant parameter in AWS Systems Manager Parameter Store.
Explanations:
The AWS::Region pseudo parameter automatically retrieves the AWS Region in which the CloudFormation template is being deployed, making it the most efficient and straightforward option.
Requiring the Region as a CloudFormation parameter adds complexity and operational overhead, as the user must provide the value manually, which is less efficient.
While it is possible to extract the Region from the AWS::StackId pseudo parameter using the Fn::Split function, this method is more complex and indirect compared to using the AWS::Region pseudo parameter.
Dynamically importing the Region from AWS Systems Manager Parameter Store requires additional setup and does not leverage the built-in capabilities of CloudFormation, making it less efficient.
From my perspective, the answer is:
Use the AWS::Region pseudo parameter.