I think Nikon Scan does better for color transparencies than Vuescan. I get nicer color. For black and white negatives, I like Vuescan better. I think both programs give equal quality for BW negs, but Vuescan is much faster. I don't have much experience scanning color negs, its been 10 yrs since I scanned one, so I can't really comment on them.
The big problem with Nikon Scan is that it has not been updated by Nikon in many, many years. On modern computers with modern operating systems it is excruciatingly slow and has a nasty habit of crashing at or near the end of a long scan, requiring you to redo the whole scan. It sucks because, as I mentioned above, NS gives better color when scanning slide film, so I tolerate it for that.
For BW I just use Vuescan. Someone posted a comparison of a BW neg scanned with Vuescan and Nikon Scan, and concluded that the Nikon Scan version was better. The grain looks sharper, but keep in mind that the Nikon Scan example he showed is much higher in contrast than the Vuescan one. Increase the Vuescan example's contrast and I bet they'll look near identical.