7850 again. Newer, about as fast, and less power hungry and less prone to heat. Plus the asus card has excellent cooling (7870s cooler does duty here also), even if it's close to the reference 7850
They trade blows as other people have stated here but obviously for asking this question you're not a fan boy of either company. I have heard that Nvidia cards have better drivers and also don't forget physx and cuda on Nvidia cards, but AMD support eyefinity your choice
yeah you should if u r geting that card cheaper then yes because it has very good cooling and overclocking and the gtx 560ti is a very good overclcoker.there is not that much big difference between the gtx 560ti and hd 7850 about 5-10% difference overclock your gtx 560ti and then you will get about hd 7850 performance and gtx 570 performance.