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 quality metrics for a plurality of streaming content sessions, each streaming content session including the streaming of electronic content from a content source of a plurality of content sources to a client of a plurality of clients, each quality metric indicating a measure of quality associated with playback of the streamed content; for a particular client that is to participate in a given streaming content session: generate a ranking of content sources based on at least some of the quality metrics and one or more content delivery costs associated with the content sources, wherein a given ranking specifies multiple content sources each ranked on expected quality of a streaming content session between that content source and the particular client; and provide the generated ranking of content sources to that client for use in selecting a content source for the given streaming content session.