^ don't listen to Malmental he's just messing around since he's an green boy. Umm I think you should get the 6870 it's perfectly fine, runs slightly on the hot side but not hotter than the 470 but doesn't OC as much as people would like.
The 6870 defiantly is a contender, it has great scaling and is improved with it's newer drivers. I think it should be your choice. If you do get the 470, I suggest getting a non-reference designed one, particularly the Gigabyte ones, however they do come at a cost. This is the best 470 out there, lower power consumption than reference, but cooler and OC'd. However, it is 300$... Sooo... yeah...http://www.newegg.com/Product/Product.aspx?Item=N82E16814125338&cm_re=gigabyte_470-_-14-125-338-_-Product
Umm as for 6870, any will do. There isn't any custom coolers like DirectCu or Hawk out for the 6870 so any brand is good. XFX has lifetime warranty and HIS/Asus/Sapphire are just good as well...
I suggest the HIS though, since it's the cheapest at 240$ but Christmas is awhile and prices may drop so keep an eye. Plus non-ref may come out.