For this comparison, I shot the same subject first with Fujifilm Pro 160S and then with Velvia 50. It was made on July 14th, 2009 at 10 pm using a 80mm lens. I shot a backlit and high-contrast scene because I was curious about the larger latidude and tonal range that low contrast negative film like Fuji 160S is said to offer.
I took an incident reading at the beach chair in camera direction. For negative film, I reduced the exposure by a little more than one stop because of the back lighting and larger exposure latitude. I shot the 160 ASA negative thus at f/16 and 1 second (EV 8). The 50 ASA slide was shot at f/16 and 8 seconds (EV 5) without compensation because I shot it a little later and the sun was already set. The shot with Velvia 50 is shown above. The result with negative film is shown below.
The subject contrast is too large for both, slide and negative film. The negative still captures the sea, the sun and the sky. In the slide, the beach chair and the beach itself are exposed correctly, but the sky and the sea are intentionally overexposed. The slide is completely white here. Looks like there is nothing beyond the beach which looks much more interesting to me than a dull sun, sea and sky visible in the negative film.
The following comparison shows a crop of the left side of each image, scaled to 50 percent. Upper part: negative, lower part: slide. Velvia looks much more vivid but not sharper. There is more shadow detail due to the over exposure but negative film does not have any better highlights.
The next example shows part of the beach, the sea and the beach chair (click to see original file). Some clipped highlights are visible at the top of the beach chair but again the color looks much more vivid. I also increased the contrast of the image from the negative film by adjusting the curves, but I was not able to obtain the same or even similar result as with Velvia. Therefore it cannot be contrast alone which makes the image appear brighter and more detailed.
Negative film is able to capture high contrast scenes and still shows detail in the shadows and highlight but this does not mean that the image looks any better. To me, slide film looks much better in this case. Sharpness is the same, both in 50% and 100% view. These and some more images are collected in this Flickr album.