Setting up a database server cluster with failover capabilities is the best solution for maintaining high availability because it involves multiple servers that work together. Should one server in the cluster fail, another can immediately take over with minimal disruption to services. Mirroring the server at a disk level will not provide immediate failover in the case of a server outage, as it only ensures data is copied. Implementing a stronger firewall does not help in the case of hardware failure but rather protects against unauthorized access. Regular snapshots are useful for data recovery, but they do not provide real-time failover or high availability.