Request routing in a network of computing devices. Back-end nodes associated with a request router send load reports to request routers. To select a back-end node for processing a request, a request router determines, based on the reports, estimated loads and corresponding errors of the estimated loads for respective nodes. A load balancing technique may be selected, based on the estimated loads and corresponding errors (e.g., round robin may be selected if the significance of an average error outweighs the difference between estimated load values for the nodes, or least estimated load may be selected of the difference between load values is greater than the average error). The selected technique is applied to choose one of the nodes to process the request. Load probability distribution may also be used for request routing, in combination with or separate from the selection based on the estimated loads.