Everyone talks about Susanoo being the ultimate defense but what about that Kyuubi chakra cloak. It's essentially the same thing. You could still get hurt if someone attacks you unlike Susanoo but it also heals you up.
While this damages in the long run so does every other great jutsu. I'm not saying it's anywhere near as strong as Susanoo but I see the two defenses headbutting later in the future.