You get Nvidia "The Way its Meant to be Played" titles and AMD "Gaming Evolved" titles.
The whole thing behind that is that AMD/Nvidia have paid the game studios behind it too optimize the game for their particular hardware or to take advantage of a feature set (obvious example would be Nvidia CUDA). However in reality, after about a week or two from the games launch it doesn't really matter that much.
Take Tomb Raider for example, on release Nvidia cards lagged in it quite badly while AMD shined because its a Gaming Evolved title. Within a few weeks, Nvidia releases a driver update that puts Nvidia cards back on par with their equivalent AMD's in Tomb Raider.