they both about the same.
gigabyte - have 2 pci if you need that , can run SLI
asrock - more USB , more sata .. and also have next generation of M.2x4.(loose SLI) so they have 2 M2 slot
all come down to it is what you need. what importance to you. i have Asrock and it been great
i use like 7 HHD , have a M2 SSD .. but trying to get the new M2x4 now (i don't SLI) ... i also use 4 USB device. i don't use PCI.
and also i only OC little .. my 4790 OC to 4.4 and so Asrock is great for me. just because of all my need.
they both great .. choose depend on what you need
( mine also happen to be on sale and rebate and combo deal so i save over $70)