Intel processors provide wonderful performance, but tend to be a bit pricey, and that pushes many people away.
Current AMD processors are cheaper, but aren't as up-to-speed performance-wise. (Which is why many have their fingers crossed for the Bulldozers, including me.)
Sometimes, though, Intel beats AMD in the bang-for-your-buck aspect entirely (which is price for performance and getting what you paid for), i.e. for a $175+ AMD processor, you'd might as well go for the $220 Intel Core i5-2500K, considering the performance boost between the AMD solutions and the Intel are more than substantial and beneficial.
I'm a complete fanatic of AMD, but I am also willing to admit that Intel processors are currently a better solution for the high-end range of computer builds, and sometimes even in the mid-range.
As for graphics cards, NVIDIA and AMD go neck and neck. Not one is better than the other, because both have their pros, cons and equal performances.