Good inquiry OP, about the most evenly matched custom cooler vs. out there right now. After time with both (two slot version for Asus), I can say that I really, really like both. A couple comparisions:
Asus cooler has a more refined contact area with a slightly better build quality. Asus has exposed heatpipes where they run unexposed with Gigabyte. Asus they're nickel plated where they're not with Gigabyte:
Fit and finish of the Asus shroud is solid and industrial, The Gigabyte is sleek and shiny and although made of plasitc, it's quite solid:
One could scrutinize further to see that one design may offer memory or VRM cooling while the other does not (depending on exact card); but from a cooler standpoint, they're very closely matched. I like the idea of two fans vs. three - fewer moving parts with Asus. Asus cooler has a slightly better build quality overall. On noise, both are very quiet under 50%, the Gigabyte a bit noisier at equal RPMS afterwards. The Gigabyte includes a very sleek PCB stiffening bar, worthy of a checkmark for sure.
Personally, I'd choose the DirectCU over Windforce all other things being equal. I like the industrial look and like fewer fans. Gigabyte's blue PCB doesn't bother me as much as some, but all black meshes better for most people. Both offer enhanced PCB designs using rugged components. Both are giants in the industry and both crank out quality products.
Curious about the inquiry, what choice do you face?