The position of your legs is going to determine the area of the quads that is most impacted. That is why some people will do front squats, box squats, sumo squats, etc. However, the difference is not as noticeable to someone who is just trying to put on mass. This comes into play more for those who are trying to shape their legs rather than build them. I always suggest right around shoulder width, keeping your feet flat, and focusing more on the motion (which can make the difference).
Good Luck.