It really depends on the age of the product. What I'm saying here is that both AMD and Nvidia make good graphics cards but some AMD grapgics cards are better than some Nvidia cards and vice versa. Usually, the newer the better but that is only in some cases.
Moreover, you cannot compare a 7 year old Nvidia graphics card to a 2 weeks old ATI or AMD card.....no matter how good the Nvidia card was back in 7 years, the 2 weeks old AMD card will have better technology and will have better chances of playing crisis 2.
Hope this helps, Rolli59