Its a matter of preference really, what looks good to one may be awful to another.
Most people i know prefer the way the stock set up of the ATI picture looks to the way an Nvidia card looks at default settings.
Equally another member may know a whole bunch of people who prefer Nvidia straight out of the box.
In older times X1xxx cards and 7 series Nvidia it was an issue that you needed to decide on as once you had the card there was little you could do about it.
These days however if you have the time and the inclination you can set up both camps cards to look near as the same as makes no difference.