i am using nvidia card but still i dont know why i think Ati is better.
my father has a computer with i3 2100,4 gb RAM,msi 5770 1 gb.
i usually dont play games on that computer but still once i tested its power and it(MSI 5770) ran every game(crysis,Dirt 3,forza,NFS HP 2010,Crysis 2 etc.) smoothly(35+ FPS) at high settings.ATI has better money to performance ratio with additional features.