These days the cards can be calibrated to look pretty much identical so colour etc isnt really relevant to most users same with textures/shaders/lighting really DX is a standard and all DX11 cards will have more or less the same set of capabilities at a basic rendering level.
Things like PhysX, Cuda, Direct compute would matter to some who use applications that utilise these things. The nvidia cards seem to have a higher tessellation ability to the AMD cards but again its not really that relevant to your everyday user. The AMD cards will do just fine.
Personally i look at performance FPS in games i like to play and most importantly value for money. I flat wont buy something i don't think warrants the price. I would rather drop some details than pay out over the odds for hardware.