Id maybe lean towards the ASRock, as it has 3 PCIE 3.0 slots, the gigabyte only has 2(and one additional 2.0 slot)
At this point in time, theres really no practical performance difference between 3.0 and 2.0, but that might not be the case several years down the line when we get into video cards that need 4,6,8 or more gigs of RAM to really push those 4K resolutions and the textures that go with them. Basically, the ASRock might be *slightly* more future-proof.
The gigabyte does have a few more USB 3.0 ports though, it has 6 on the back panel as opposed to ASRocks 4. Both support up to 4 USB 3.0 ports in the front as well(if your case is designed for it)