REST vs. gRPC for internal microservice communication: factors to consider?

Our team is designing a new set of microservices and we're debating between using REST (HTTP/1.1 with JSON) or gRPC (HTTP/2 with Protobuf) for inter-service communication. For external APIs, REST is the clear choice, but internally, the performance and strict schema of gRPC are appealing. However, gRPC also introduces a steeper learning curve and more tooling overhead. What are the key factors you consider when making this decision for internal services? Are there specific scenarios where one significantly outperforms the other beyond just raw speed? I'm particularly interested in operational complexity and debugging experience.