1. A system, comprising: one or more memories; and one or more processors coupled to the one or more memories, wherein the one or more memories comprise program instructions executable by the one or more processors to: receive, at a computer system from a plurality of remotely located clients, wherein the computer system is separate from the plurality of remotely-located clients, quality metrics for a plurality of streaming content sessions, each quality metric indicating a measure of quality of playback of streamed content of the streaming content sessions; generate, at the computer system, a ranking of content sources based on at least some of the quality metrics, wherein a given ranking specifies multiple content sources each ranked on expected quality of a streaming content session between a respective content source and a respective client; and provide the generated ranking of content sources to one or more clients for use in selecting, during a first portion of a given streaming content session and in response to performance degradation of a first content source, a second content source to switch to for a second portion of the given streaming session.