Both are great, quiet and cool, you can't go wrong with either.
Keep in mind that if you play games that use PhysX (Mafia II for example), will run better with the GTX460. If you have multiple moniters, take advantage on Eyefinity with AMD.
If you would like a preference, i would choose the GTX460 because it performs better in the games i play, i don't need Eyefinity, and i like PhysX . You may be interested in doing some research to see which is better in your games, but at the end of the day, it won't make much of a difference