The 7850 is the better card for gaming ... because it is a newer card that can run games on higher settings while maintaining playable frame rates.
To those who say the GTX 560Ti has more stable drivers .... NOT necessarily. My computer (with a GTX 560Ti) randomly crashes while playing youtube videos on the latest NVidia drivers! and this is a card that is over a year old already!! AMD drivers will also have bugs and problems ... but its not like NVidia is perfect in comparison.