2D, because I don't buy into the marketing hype that is 3D.
It's an old technology that gives people headaches, gives film makers and studios some quick money by doing a few generic 'OMG STUFF POPS OUT OF THE SCREEN' shitfests while the kids who don't realise how old the technology is are still wowed by it, and gives cinemas an excuse to inflate ticket prices. That's all. There's nothing more to it.
You can't do anything artistic with it, and unlike colour, you can't use it to simply enhance the picture and make it look more realistic because fake 3D doesn't look realistic at all. It's just a stupid gimmick and that's all there is to it.
It died off before, and hopefully it will die off again.