Quay.io has been outstanding for us so far. Much better overall than Docker Hub for our organization. Particularly in ergonomics and team/permissions granularity.
To worsen the issue, Quay still doesn't seem to support parallel layer downloads, and Docker 1.9 even complains that "this image was pulled from a legacy registry. Important: This registry version will not be supported in future versions of docker."
I just ran a quick test (way off peak time) and Quay was 2.5x slower than Docker Hub for an image built from the same Dockerfile.
I'm looking forward to more usable international service at some point, but right now it just isn't really worth it.