If you are going to keep it 5+ years I say buy new, get exactly what you like in perfect condition. @YARNLADY is right that the second you drive a new car off the lot it depreciates like crazy. So, financially it is better to buy a used car, but I think you need to look at all the factors, not just that one.
End of year prices are better. Once they start receiving the 2013 models they will want to dump their 2012 models. The only negative with that is you have to usually choose from a car they have on the lot (if they have multiple dealerships in a region it could be from cars they have at any of those dealerships) so it limits color choice and upgrades. Most Japanese cars have upgrade packages, so it is less of an issue with cars like that, because the cars tend to have similar features. Oh, there is one other negative that if you want to sell it in a couple years, the model year will be older obviously, even though it was not driven until the end of the year. But, if you plan to keep it 4+ years I wouldn’t worry about that.
I don’t recommend demos, only because people kind of abuse them sometimes. My husband once bought a demo, and it was ok, but I still shy away from it.