Which tool is best suited for gaining information about all virtual machines and storage containers in a cloud environment?

The best choice for gaining information about all virtual machines and storage containers in a cloud environment is ScoutSuite. This tool is specifically designed for auditing and gaining visibility into cloud service configurations across multiple platforms such as AWS, Azure, and Google Cloud. It provides a comprehensive overview of security posture by collecting data on various services, including virtual machines and storage containers, and presents this information in a way that helps identify potential security risks.

Nessus, while a powerful vulnerability scanner, mainly focuses on identifying vulnerabilities on local networks and systems rather than being tailored for cloud environments. Arachni is an open-source web application security scanner primarily for web application vulnerabilities and is not suited for cloud infrastructure auditing. OpenVAS is also a vulnerability scanner like Nessus, and it is not specifically designed to handle the nuances of cloud infrastructure, which can include a wide variety of virtual resources and containers.

Thus, ScoutSuite stands out as the most appropriate tool for obtaining detailed information about virtual machines and storage containers in a cloud setting, making it the ideal choice in this context.