I've used both actually. While I get the desire to compare the two, the experience is so different that I don't see them as competing projects.
The CastAR does very well as augmented reality. You have the screen in front of you with great visuals on it. The 3d effect is really nice and the positional tracking is impressive. Its strong points are that it can be used by multiple people at the same time, and the fact that it doesn't make you motion sick (it isn't immersive enough). I would choose this for product visualization or casual gaming.
The Oculus rift is VR only but has a much wider field of view. You are completely immersed into your environment. This can cause motion sickness in some people, but that is getting better as the tech gets more accurate and high resultion. I would choose this for Virtual reality experiences any day.
I guess I should point out that the CastAR does have a VR attachment to allow it to do the more immersive VR experience. I haven't tried it yet though, so I can't vouch for the results. If it is anything near as well done as the AR though, it will be impressive.