The Reliability pillar of the AWS Well-Architected Framework is the most appropriate to emphasize for handling changes in load automatically and avoiding service interruptions. This pillar encompasses the ability of a system to recover from infrastructure or service disruptions, dynamically acquire computing resources to meet demand, and mitigate disruptions such as misconfigurations or transient network issues. While Performance Efficiency is also concerned with resource allocation, it is more focused on the efficient use of resources rather than ensuring continuous operations and recovery from failures, which are central to Reliability. The Security pillar is about protecting the information and systems, which, though essential, does not directly address the stated concern of handling load changes. Operational Excellence mainly deals with running and monitoring systems but does not directly ensure the system's capability to handle unexpected demand spikes.