Theres not masses to choose form, where one dips vs. the other, then it compensates in other places.
After a brief look, Main things are:
- Is there much / any price difference? Would that way in your favour?
- The Asrock can only support the Higher RAM when overclocked, where as the Gigabyte can support them all (Up to 2133)
- The Asus has a HDMI port at the rear, the Gigabyte does not.
- The Gigabyte board supports a lot more RAID features, if you are seriously into security / back up
- More 1.0 + 2.0 USB ports on the Gigabyte
- No PCIE3 Slot on the Gigabyte (Wont be as 'futureproof' down the line)
Me, personally, I would be going with the gGgabyte board. The support and assistance in general from Gigabyte (In most of my personal experience is very good, better than Asus anyway - off course you can experience different problems everytime, so it could be vica versa in some cases!), so that would be the main deciding factor for me..
Also it depends on what you're doing, and how important things like the PCIE3 slot, and ports etc are to you. Not masses in either to be honest, both pretty solid boards.