I have no idea why you'd say that "it's very well known" that AMD-based cards are better. It isn't, and they aren't. Their recent generations tend to have less stable drivers, use more power, and generate more heat. That's why I ended up spending (very) slightly more for an equivalent nVidia-based card the last time I bought a video card. That, and the last two AMD-based cards I've owned have caused me no end of headaches with multi-monitor setups and connections to TVs, which has made me a bit gun-shy about buying AMD-based cards lately. It's not a matter of price...nVidia hardware tends to be a bit more expensive (although, depending on the GPU the price difference is usually not huge).
Don't get me wrong...I think that AMD has done pretty well and their GPUs and reference designs are perfectly fine, but to say that by some absolute measure one company's designs are better than the other's and that there is some kind of consensus about this among users is certainly inaccurate.
http://www.anandtech.com/show/7481/the-amd-radeon-r9-290-review/15
Anyway, I'd like to see AMD do better. Competition is good...both for innovation and pricing.