But anyways, yes an elliptical.

Treadmill would be the better workout, but lets be honest, barely anyone wants to run often. I run a couple times a week and I hate it.

If you learn to configure it right, an elliptical can give a damn good workout, with minimal shock to joints.

Biking is great, but I don't think it's as great of a workout as people think. It can be, if you're hitting trails or doing hills, but I ride 50+ miles per week commuting to class, and shit if I notice any health benefits from it.