Just want to know which company has better support for TES series? I heard Oblivion runs better with Radeons, which one do you think is better for Skyrim?
Well, my opinion is both... really. Whatever your choice, your GPU must support direct X 11; and crossfire or SLI. You have to buy at least one GPU with 1 GB, GDDR 5 and HDMI to run Skyrim in good condition i'm afraid. See Tom's Hardware to compare performances.
Also, if you buy a new computer, always buy a very good power supply prepared to receive future updates on your system. Also i recommended a Quad core CPU and Windows7 x64.