Which is better Multi-AZ DB Cluster or Multi-AZ DB Instance for Amazon RDS for PostgreSQL

• First question, what’s the requirement?
• Is there a budget?
• What’s the balance of reads and writes to the database?
• Is there an RTO?
• have you considered Aurora Postgres?

One gives you a warm standby while the other gives you 2 read replicas with failover.

Multi AZ instance Support high availability for your application with automatic database failover that completes as quickly as 60 seconds with zero data loss and no manual intervention

Multi AZ Cluster This is a database cluster with one primary and two readable standby instances. It provides up to 2x faster transaction commit latency and automated failovers, typically under 35 seconds.

Here’s a good article to read https://aws.amazon.com/blogs/aws/amazon-rds-multi-az-db-cluster/