If you want strength and power then you should squat and deadlift (powerlifting moves and not body building or shaping / conditioning moves). Look up periodization. No drugs, 8 week cycles, once a week on each lift as heavy as you can in the cycle while maintaining your form. Done correctly, you will gain power and speed. I never bought into the single leg anything because you can not lift as much weight, are at a greater risk of injury, and thus delay your progress. You have to be careful to not overdevelop a specific muscle group or you risk injury. Squatting and deadlifting will work all muscles the way the body was designed. Ever wonder why kids pull hamstrings? Typically related to overdevelopment of the quad and not enough development of the hamstring. They are out of balance and one will tear.