I seem to not be able to do that much weight on the hack squat compared to the leg press (which makes me believe that it is a good exercise). Now I've been doing squats (at a lite weight) and well, my hips are disproportionate. I have one foot slightly longer than the other, and one leg a tad longer than the other. So when doing squats it kinda hurts my knees (they start to pop really bad, and I keep getting weird bruises on them). I'm starting to reconsider doing squats and just replacing it with the hack squat machine (since I don't really have a problem when using it).

What is everybody's opinion on the hack squat? Is it solely a quad exercise or does it work the hamstrings too?