Before the Kyuubi just took over Naruto (with his consent).Interesting topic.
We've seen that Killer Bee can control the Hachibi, but the Kyuubi is much more sinister. Being the nine tails, it's certainly the strongest, and falls just below the ten tails. On top of that, with Naruto's fiery attitude and the way he can explode with anger, it often allows the chakra of the Kyuubi to leak out without Naruto's consent =/