If you're looking to focus more on the quads, an upright torso position is best.
Taking a longer stride (with a vertical tibia) is more hip-oriented version; taking a shorter stride with a slightly angled tibia is a more knee (quad) oriented version.
So, if you're really trying to hammer the quads, you'd combine an upright torso with a slightly reduced stance length that creates a tibia angle similar to one involved in a standard squat.
Finally, some ammo to use against those putzes who insist on benching with their feet in the air. Craig also makes the case that chin-ups are a better lat exercise than pull-ups. Let the arguments begin!