Which AWS service should the company use to obtain these recommendations?

Explanations:

AWS WAF (Web Application Firewall) is primarily used to protect web applications by filtering and monitoring HTTP traffic, not for assessing security best practices across the AWS environment.

AWS Systems Manager is designed for operational management of AWS resources, such as automation, patch management, and inventory. It does not specifically provide security best practice assessments.

AWS Trusted Advisor evaluates the AWS environment against best practices in several categories, including security. It provides recommendations for improving security posture by identifying gaps and suggesting remedial actions.

AWS Shield is a managed DDoS protection service that safeguards applications from DDoS attacks. It does not offer a comprehensive analysis of security practices or recommendations for the overall AWS environment.