Well, tbh, they are all very good companies and make amazing products. It also depends on who released what last. Currently, Nvidia is the dominator of GPU's right now due to the recently released GTX 970 and 980. Intel is also the dominator due to the recently released DDR4 8 core behemoth of a CPU, but AMD has yet to even touch ground in these areas with new products.
Personally, I like AMD because I can replace my CPU if I need to without having to shell out an arm and a leg.