Via at default, NForce to overclock. The trouble with NForce is that for an overclock to beat Via you will need to do volt modding. If you are not afraid of that go for NForce. For a stable overclock without extreme the choice should be VIA.
And not all boards are the same!
Via: Albatron, Epox, Asus.
NForce: Giga-byte, Shuttle.
Personally I have two Asus K8V deluxe and I find these, without exaggeration, some of the best and the most stable boards I've ever had. Both are retail, I learned lesson buying "refurbished."