I think aerobics at night is much better. In the a.m., first of all, i get extremely nausuas if I do cardio and there's nothing in my stomach. So then if I eat something as I wake up and do cardio like running, I'll easily get a stmoach ache. My gym, for instance, is open till 11:30 at night. So, generally, I'll eat dinner at like 6:30 or 7:00, and workout from maybe 9:30 to 11:30. I have the energy because there's food in my stmoach, therefore, I am able to workout at a greater intensity. Also, nothing feels better than being able t0o lie down and go to sleep after a hard workout.