the HD4870 currently kicks ass every nVidia video card :) and the HD4780X2 is way better than the 4870 XD but, ATI often screws up with drivers allowing nvidia to catch up *sometimes*
It seems to me that more developers are focusing in working with Nvidia cards and thus have fewer compatability issues. I enjoy the competition, dirving performence up and $$ down :)
Currently using an Nvidia 8800gt because I bought my video card at the start of the year, but at this point in time the 4780's are the top dog, so ATI for now.
ati 'cause of the new hd 4780 x2 with 2gb ddr5 and the best price more low than an nvidia 9800x2 atm is the best graphic card in commerce but i think nvidia soon will create a new card too