Various embodiments of a system and method for assignment and switching of content sources for a streaming content session are described. Embodiments may include the generation and use of content source rankings for improving playback quality of content streams. In embodiments, a merchant system may collect and aggregate multiple quality metrics for different content streams that various content sources provide to various clients. The merchant system may utilize the quality metrics to generate rankings of content sources for clients. The merchant system may provide such rankings to clients to improve the content stream playback experience on the client. For instance, at content acquisition time, a client may request a content stream from a content resource ranked highest on a content source ranking provided by the merchant. If the content stream degrades, the client may source subsequent portions of the content stream from another highly ranked content source of the ranking.