Angled leg press doesn't suit me at all, I go down 4 inches and that's where my range of motion stops, I wish I could do them deep enough to be useful, I think it's a machine that isn't so mentally stressful while still stimulating the quads. Different horisontal presses suit me fine. Regular squats are fine, except I can't quite break parallel, which you don't necessarily have to do to build quads, but just saying. Lower back is fine as far as squats, I can do tons of weight on good mornings, much more than on squats. Squats on smith machine solves the depth problem. I have loved box squats as a strength building move for deadlifts or just lower body strength period. No issue for the lower back ever, maybe because my lower back is so relatively strong. I still maintain that the reason many injure or tweak their lower backs on squats is because they don't really strengthen their lower backs in their routine, maybe abs as well, but I'm biased.