The best choice for unpredictable and variable traffic with spikes is a compute service that scales automatically without requiring manual intervention for provisioning or managing servers. This is where serverless computing shines, as it abstracts the servers away and automatically adjusts to the traffic. Lambda fits the bill as it automatically manages the underlying compute resources. While EC2 instances can scale, this process is not as immediate or seamless as with Lambda. Fargate provides a serverless container experience, but it still requires some configuration for scaling and does not scale as responsively as Lambda for sudden spikes. ECS on EC2 instances also provides scalability but requires more hands-on management compared to the automatic scaling provided by Lambda.