ASRock is cheap-ass brand of Asus. Basically comes from same factory except using 2nd grade components. You get exactly what you pay for. ASRock is by far the best choice of motherboards if you want to build on very strict budget, but those will lack certain features if you want something special. Also ASRock is one of the biggest OEM board manufacturers for big brand computers like HP.
Raiding is very CPU-heavy, as well as hanging around in busy cities (like Dalaran now). Solo content depends more on GPU.