I would absolutely go with the Gigabyte over the ASRock.
Although I have been seeing the ASRock's been getting better reviews recently, this is a new trend.
Gigabyte has been battling with Asus for years to be the most stable / best boards, and they do a great job.
Usually the only reason people go for ASRock is they are generally a bunch cheaper. If they are at the same price point, I would go Gigabyte.