Which Google Cloud platform should you use to run a Go 1.12 HTTP(S) API with highly variable traffic that must scale reliably and require minimal operational overhead?

App Engine standard environment is the best choice for this scenario. It offers automatic scaling to zero, which is ideal for highly variable traffic, and requires minimal operational overhead because Google manages the underlying infrastructure. Go 1.12 is a supported runtime. Google Kubernetes Engine (GKE) provides great flexibility but requires more operational overhead for cluster management and scaling configuration. A Managed Instance Group (MIG) on Compute Engine also requires more operational overhead for VM and scaling group management compared to App Engine standard. App Engine flexible environment offers more customization with custom runtimes but has higher operational overhead and doesn't scale to zero as efficiently as the standard environment, making it less suitable for minimal overhead and highly variable traffic.