Well, let's see. In my life I've been through plenty of motherboards from a host of different manufacturers, and this is what I have to say. My old Asus Intel 440BX motherboards are still alive and kicking after 4 or 5 odd years of running and they're stable, the new Asus boards seem to be on par with these old ones when it comes to stability so they've got my vote there.
In contrast I've gone through no less than 3 Gigabyte ( 4 counting trade-ins for warrenty ) K7 motherboards, and that kinda destroyed my opinion of the company. If the new boards prove me wrong, then I'll be a fool for letting them go, but I don't recommend it.
My current star however is MSI. I currently run the MSI K7N2 Delta ILSR nForce2 Ultra board, and it's nothing short of perfect. If the K8 boards match up, I'll probably be buying an MSI. And as a matter of interest, I live in South-Africa, and here MSI boards are cheaper than most any other manufacturer, just beacuse of availiblity.
Seriously there are lots of manufacturers out there. And you can't really just say, mine is the best, rather say mine is the best for me, it might be for you. :P | 
