I'm really not happy with my dfi 790fxb-m2rsh anymore, its unstable, the raid is slow, memory wont go to the right clocks, sound is broken. It's been rma'ed once to fix a cracked chipset and they charged 60$ to do it even though i hadnt touched the heatsink on it or anything.
Msi is my first choice, followed by the ecs board. I've used msi's rma process, but it's been a few years since I needed it. I've been able to overclock the msi low end boards, such as the 6150se or g31 when other brands wouldn't.
The ASUS already officially supports the X6. The MSI does not officially support it, but has a march bios update that appears to be the X6 support. Both boards support 140 watt chips and have heatsinks on the MOSFET's.