Asus produces better quality products which are stabler and last for longer. SFAIK the Asus is the best followed by the MSi as Helltech said, The MSi will come in cheaper than the asus more likely however while not sacrificing a noticeable amount of quality.
I also recommend EVGA however there inline with Asus expense wise.
I currently have a 9800GT LPE from Galaxy, Ill be upgrading to a HIS or similar 6xxx series card soon.