A company has a website that is developed in PHP and is launched using AWS...

The Immutable deployment method is the best choice when a company requires minimal downtime and automatic rollback in case of a failure. Here's why:

In Immutable deployments, a new set of instances is launched with the updated version. These instances are tested and validated before they replace the old instances. This ensures zero downtime and immediate rollback if the deployment fails.

All at once (A) causes downtime because the update replaces all instances simultaneously.

Rolling deployments (B) update a few instances at a time, but if a failure occurs midway, downtime or partial unavailability can happen.

Snapshots (C) are not a deployment strategy in Elastic Beanstalk.