The 'Enterprise Support' tier is the appropriate choice as it offers 24x7 access to Cloud Support Engineers, proactive guidance through a Technical Account Manager (TAM), and infrastructure event management services, which are essential for an organization with mission-critical deployments and the need for constant technical assistance and event planning support. The 'Developer Support' and 'Business Support' tiers do not offer the required level of assistance such as direct access to TAMs or infrastructure event management services, and the 'Basic Support' and 'Enterprise On-Ramp Support' tiers are designed for smaller scale operations with less direct and less proactive forms of support.