They all have issues once in a while. None is really head and shoulders above the rest. We've run up to 5 CDNs at once for very large events and still had issues.

Taking a pragmatic approach the questions you need to be asking are more like "what is my actual uptime target?", "what benefit is this piece of my architecture adding?" and "is the cost (in terms of complexity if not actual money) worth it to diversify?"