I use uni-WB with my D300 and I have the hardest time getting the colors to look "right" with ACR; in fact, it's almost impossible. So for quick and easy conversions with a minimum of fiddling, NX works much better for me -- in part because I spent some time developing the adjustments and work flow to get the most from my files (there is a learning curve with all converters); with ACR I spent about a year fiddling with the adjustments without much success, and when I bought Capture One LE it took about a day to start getting consistently better colors with my D200, plus Capture One LE delivered more detail than ACR.
Another consideration for me is that I got my version of NX free when I bought my D300 and upgrading ACR requires me to spend $300, so it actually costs me more to use ACR than it does to use NX. Likewise, Capture One LE was upgraded for free so I still spent less than $100 for that converter.
I'm not wedded to NX and will consider using whatever converter delivers the best image, but I have never seen the best image for my Nikon DSLRs coming from ACR; sometimes I prefer Capture One, but almost always it's now NX. I was using Raw Magick Lite with my D200 which only cost $35, but unfortunately that program was never upgraded to handle D300 files. I would probably jump on Raw Photo Processor if I had a Mac, but right now I'm still using a PC.