FYI, you can just call it AMD now.
This was in the news this morning.
I'm gonna assume Phobus will correct me, bc it seems any tech topic I comment on, he's right there with me so...
If you're looking at PC Gaming, and looking at the latest news with which video card being the best and fastest, AMD and nVidia have been flip-flopping the crown now for the past two years or so, when AMD/ATI (at the time) wasn't able to beat the 8xxx series and 9xxx series from nVidia. So what AMD/ATI did was aim to undercut their competition by making good/fast video cards for lower prices. So if they couldn't get the fastest video card crown, they could get the best bang-for-the-buck crown (as well as selling a lot of cheap video cards, but that's a different matter).
Anyways, AMD/ATI had a re-envisioning of their product, and there's a couple reasons to look at going AMD/ATI over Intel/nVidia (or Intel/ATI; AMD/nVidia).
1) Price: From reviews that I've seen (from tomshardware.com) most of the mid-range video card wars are won by AMD due to its pricing and performance. nVidia may do better, but cost $40 more. And when it's $40 more, it then competes against a faster AMD GPU, thus losing. However, pricing always changes so its an argument you can base only on the present, and hopefully an educated guess about future prices (supply vs demand) for the video card.
2) Relationship: Wayyy back in 2004, 2005, the harmonious relationship for CPUs/GPUs was AMD/nVidia vs Intel/ATI. Then AMD bought ATI out for $5.4 BILLION dollars. Fast forward several years, and AMD and ATI have learned a few lessons: A) ATI wasn't worth the $5.4 Bn buyout. If anything, it was more likely worth $2 Bn for AMD, though stock prices and ATI's GPU market share was higher and more successful pre-merger (it sunk post-merger), B) AMD has successfully incorporated ATI's personnel into its ranks, C) There are new technologies and products emerging from the merger that means AMD video cards will work better with other AMD products.
3) Fanboyism: The weakest reason for them all, but hey, some people just always cheer for the team they want to love (or want to hate).