I'm no expert, but since STR scaling is so much better, why would you favor DEX in a quality build?
Well it used to be that you only need to put 27 points in STR to get the maximum 40/40 scaling, since the STR increase for 2 handing a weapon in DS1 applied to both the weapon requirements and the scaling value, but I remember someone in here saying it didn't work that way in this game, so 40/40 STR/DEX would probably be a true quality build now.