Here's the thing. You've entered a sweepstakes and the prize is "any current Nikon DSLR." Which one do you take?
We have a couple of variations on how to play the game.
First up, DX only.
At the end of 2014 your choices were D3300, D5300, D7100, and D300s. The D5300 has the swivel LCD, the D7100 has more features, and the D300s has the most features, best build quality, but can't match the others in image quality.
The choice for me is easy: take the D7100. The only things you give up is the swivel LCD of the D5300, the buffer/buttons/build of the D300s. You get the best image quality and close to the best feature set, though.
Will the answer change in 2015? Almost certainly yes. We’ve got at least two DX DSLRs coming during the year (D5500, D7500).
Next, let's try FX.
At the end of 2014 your choices were D3x, D4s, Df, D610, D750, and D810. That's a much tougher choice, because those cameras are all over the place. There's also the clear option of taking the most expensive camera, selling it, and buying a less expensive one ;~). But I'm going to assume that you're stuck with the one you choose.
You can't pick the D3x because the D810 is better in image quality, and the build quality difference just doesn't justify picking the D3x, even if you love vertical grips (you can always add one to the D810).
You can't pick the D610 because the D810 is better in image quality, features, and to a small degree, build, while even the D750 is better in focus and features.
If you're always shooting at ISO 3200 and above and/or you need very high frame rates for what you shoot (e.g. sports), then you clearly pick the D4s.
The only reason you pick the Df is probably because you like dials. (It's not better in image quality than the D810; it's not better in frame rate, features and build of the D4s.) I write that a bit sarcastically, but the only other thing I could come up with is that it's a bit smaller and lighter than most of the others, or you are shooting above ISO 3200 an awful lot and don't care about frame rate or focus system. Most people aren't going to pick that way, I think.
Many people should pick the D750. It’s a very well balanced camera that’s got Nikon’s latest technology and image quality tweaking (JPEG). The small size and light weight coupled with the swivel LCD were a nice surprise.
Will the answer change in 2015? Well, if you were choosing a D4s in 2014 you'd choose a D4s in 2015 ;~). Other than that, I'm not sure. It doesn't seem like a year when we'd get new iterations of the D750, D810, or Df. Perhaps a D4x might appear, and that might change the equation.
Now it might seem silly to play this game, but it does have a function. One of the questions I get asked every day is "should I buy an X or wait?" Okay, play the game. What's your answer for 2014? Now how likely is it that 2015 will change your answer? Right now it's only the D7100, D300s, and D3x users that have a high probability to have their answer change in the coming year, I think. If you picked something else, then the answer is most likely "don't wait."
So how long should you wait? New DSLRs will come in January, February, and August, I think, with the much slimmer possibility of one late year arrival, as well.
Stay tuned for The Nikon DSLR Sweepstakes Game, 2015, coming to you in January 2016.