We all have those days when we've only penciled in a small amount of time to hit the gym. So on the days when you're short on time, which machine will give you the most bang for your buck?
In general, if you're crunched for time, pick a cardio machine that puts both your lower and upper body to work. This can be done by using machines such as ellipticals or Arc Trainers. As long as you don't let using your arms slow you down (intensity wise), pumping the handles allows you to work your upper body, which gives it a slight calorie burning advantage over cardio machines without handles.