The only real difference between the two, in my opinion, is their phase design. The asus has 4+1 and the Gigabyte 8+2. Everything else is similar, though I'd say the cooling of VRMs is better on the Gigabyte as well. They both have 1 x16 and 1x4 PCI-e slots.
My vote goes to the Gigabyte, for potential overclocking capability with 8+2 design.
EDIT: Bolded, too. heh, Bb