Availability Zones within a single region offer high availability and fault tolerance against most failures but do not protect against region-wide outages, making them a cost-effective solution for applications that can tolerate such risks.

Deploying across multiple Azure regions provides the highest level of fault tolerance, including protection against region-wide outages, but introduces higher costs, increased complexity, and potential latency issues.

Using Availability Zones is always the best choice for all applications because it guarantees 100% uptime and is the simplest to manage, regardless of the application's requirements or budget constraints.

The choice between using Availability Zones and multiple regions should be based solely on the company's current budget, without considering future scalability or compliance requirements.

Both Availability Zones and multiple regions have their place in a comprehensive high availability strategy; the optimal choice depends on the application's specific requirements, including tolerance for downtime, budget, and compliance needs.