As was already noted, the Rage is the stronger ball - at least in oil. I have played with the surfaces on both balls, and I believe the Rage is also the most versatile of the two. With a rougher surface, the Octane does become a little more controllable and handles the oil better, but I think the Rage is better for that task.
That said, the Octane is definitely the stronger of the two when it finds friction. It is definitely a ball that you need to be more consistent with your shot making. It can be a deadly weapon - both positively and negatively. Unfortunately, I've seen both ends of the spectrum lately.
You do need some oil with both balls. The difference is, you can play more through the oil with the Rage. You need to get the Octane to the friction. But at the same time, you don't want to get it there too early. As much as I've been using the Octane lately, if you have the oil for it, go with the Rage. Then consider the Octane as a ball to go to when the lanes breakdown and you can get left and swing it right (assuming you are right handed).