Really up to you on choice.The HIS and XFX cards come with DIRT 3 which is always a good bonus.Also I've seen that the HIS IceQ X Turbo's heatsinks is acutally quite good.
So that might be something to think about also.
Yea, I was tied between the 6790 and the 6850 but i think ill save some money to get the 6850 instead. Again tho, what brand? XFX is preferred but i get confused when someone recommends another brand like the Power Cooler wintermint suggested.