I always get asked "Which card is better" and frankly it's all a matter of personal taste.
If you want to get a comparison between two Video Cards (ex. ATI and GeForce of the same class or a lower class vs a higher class video card) I'd suggest using http://www.gpureview.com/ .

This site has all you need from all the specs to user ratings.You can even see what overclocking does to the cards.