FIRST HAND INFO:
All I can speak to is the fact that the 1.8G is a workhorse on my D7100. Nice bokeh, sharp focus, easy touch-to-fine-tune manual focus ring. I have no complaints.
SECOND HAND INFO:
A lot of research (God Bless Google) in a few minutes shows the 1.8G to be consistently sharper than the 1.4G through f8, even with it through f11, and slightly behind at tighter apertures (but not a lot). Most places call both lenses "incredibly sharp" though, so I doubt most folks would notice the differences mentioned above. I'd call it a tie.
The 1.4G gives a slightly smoother bokeh look, but on most of the comparison photos I found, it wasn't immediately noticeable, and most reviews called it negligible. Taking the time to compare side by side, though, the 1.4G wins that battle, but only slightly.
A LOT of reviews mention how much slower the 1.4G focuses when compared to the 1.8G. I haven't compared them personally, but if so many people are saying it, there must be something there? All I know is my 1.8G locks focus in half a heartbeat in most situations... even if the 1.4G took twice as much time, it still couldn't take THAT long, could it?
LONG STORY SHORT:
With prices that close to each other, I'd probably buy the 1.4G if they're all in good condition, but you definitely won't be disappointed with the 1.8G if you go that way, and you'd save $75.00. I'd also say that I'd take either of the G series lenses over the D's there any day of the week.