I would go with the GIGABYTE
Why do you say that? While I know Gigabyte is a reliable motherboard company, ASRock is too.
Oh and another difference: RAM support:
The ASRock Support DDR3 800/1066/1333/1600
by default but is limited to only 8GB max
while the Gigabyte only supports DDR3 1066 natively with 1333 support if you OC
but has double the max memory (16GB)