I am setting up a home gym and I am looking at getting a piece of equipment for cardio (though if it helps out other muscles I am fine with that). I am a mid twenties male so my body can take a bit of a beating, but I don't want to get a machine that will end up injuring me when my goal is to get in better shape (ie I've heard treadmills can wreck joints). I have narrowed my choices down to two machines either a Nautilus NR3000 Recumbent Bike or a Concept2 Model D Rowing Machine. I think both are high quality but which form of exercise will get my overall body into the best shape in a healthy way?