IMO one of the best "shaping" cardios is HIIT on stairs. It hits all of the muscles in the lower body hard enough to make them grow. A lot of times hamstrings/butt/calves can be neglected, or not worked as hard in cardio as the quads, but they do very nice things to your figure. Gotta love the short shorts and mini skirts Who notices your slightly soft belly when you've got show stopping legs and glutes?