I tried the Oculus Rift at a community tech event last summer/early fall. It was the Dev Kit 1, and I found it somewhat underwhelming. I've read that for about half of people, it did not have sufficiently high resolution to feel immersive, and I fell on the not-immersive side of that rift (pun intended). To me, the screen-door effect was far too noticeable for it to be immersive, and it felt like I was playing an old game with low-res graphics. To be fair, one of the demos did have some kind of neat 3D effects with snowflakes and cobwebs, but on the whole it didn't make the impact I expected.
I could see how for some people there might be nausea issues. While I didn't have any in the short time I experienced it, I did have a feeling afterwards like I'd just stepped off a boat. Which, when you multiple it by a few and add more fast action-packed sequences, could be heading straight towards seasickness.
The Vive does sound a lot more advanced. Project Morpheus (Sony) also sounds as promising as the Rift (though according to Kyle Orland, less so than the Vive). It's still early days, though. At this point, I'd still want an in-person demo of a newer system before thinking about buying any of them.