I have built three computers with ASUS motherboards, my #2 with a P5A and K6-3 400 (which I still have, oh the nostalgia), my #3 with an A7V and Athlon 1.2 (plenty fasst), and my friends with a A7V-133 and Athlon 1.2. It's just that I was so impressed with my P5A that I look first to ASUS.
My next MB will be an ASUS or an Abit. In my experience, and I am a thoughtful person, what I see is very good and stable hardware and rather sloppy and unreliable software (that includes drivers). I have never, I don't think, ever had a hardware problem, it has always turned out to be a software issue.
I base all my purchases on reviews, by the way.
Reliability is simply a requirement.