I have the ASROCK Extreme4 and was thinking the same thing before I purchased. I am very happy with the ASROCK. It has a power switch on the motherboard and a LED light that shows errors and such built into the MB. I am very impressed with this board.
The Asrock, for sure. Not only the above mentioned points, but if you ever add a 2nd card on the Asus, you will probably loose some of your SATA ports. A long card will cover just enough of them to make it impossible to plug in a cable.
Also, the Asrock appears to have better quality solid capacitors.