Gigabyte - never a single problem on my nforce4
Many of my friends had Asus boards, and they all had some issues, always something else...
Memory fried, gameport didn't work, raid failed (!), southbridge coolers failing, agp ports frying new vga cards... on and on.
And when it happens, it's always: "maybe I just got a bad sample, Asus mobo's are great!"