What is the MOST comprehensive tool that will accomplish this task?

Explanations:

AWS Cost Explorer provides detailed insights into your AWS spending patterns. It allows you to analyze and break down costs by service, account, region, or linked account, which is essential for identifying cost drivers and trends in billing.

AWS Trusted Advisor is primarily a service that provides best practices and recommendations for security, performance, and cost optimization. It is not designed specifically for detailed cost analysis or identifying billing increases.

Cost allocation tags help in categorizing and tracking AWS costs for specific resources but are not comprehensive for deep billing analysis or identifying trends over time. They are useful for managing and allocating costs, but they don’t provide a full cost breakdown.

Resource groups allow you to organize and manage AWS resources, but they are not focused on billing or cost analysis. They are used for resource management, not for identifying billing increases.