Techniques for a service provider network to generate suitability scores that indicate how well VM instance types are performing given the workloads they are running. Using these suitability scores, users are able to easily determine the suitability of VM instance types for supporting their workloads, and diagnose potential issues with the pairings of VM instance types and workloads, such as over-utilization and under-utilization of VM instances. Further, the techniques include training a model to determine VM instance types recommended for supporting workloads. The model may receive utilization data representing resource-usage characteristics of the workload as input, and be trained to output one or more recommended VM instance types that are optimized or suitable to host the workload. Thus, the service provider network may provide users with easily-digestible suitability scores indicating the suitability of VM instance types for workloads along with VM instance types recommended for their workloads.