I'm using a D7000 and I'm looking into getting a nifty fifty. I'm kinda deciding between the f/1.8G for retail price (~220+tax) or I can get an used f/1.4D for $170. Which one would you recommend?
Assuming you don't care about the price difference...
The f/1.4d is two-thirds of a stop faster than the f1.8g and it has the aperture ring. You may or may not care about the aperture ring, but some people do. Those are the obvious physical differences.
At any rate, Photozone has reviews on both: 50mm f/1.4D and 50mm f/1.8G and the f/1.8 is generally sharper at the same aperture. Given the low light performance of the D7000, which will help counter the difference in aperture, I would likely tend to the f/1.8 as it is a bit better from the optics perspective.