I got no experience on both manufacturer ~
But if u based on spec , Asrock Z87 Extreme 4 got better on-board audio chipset ~
Others spec , they are quite identical.
And if u care about how the mobo looking , Gigabyte GA-Z87X-UD4X , which I think it got better looking ~
Btw Asrock cheaper is because its only got 1 year warrenty for its product , if I didnt remember wrong so it can cut cost and better chipset on the mobo ~