it really boils down to a preference thing in the long-haul. There are several theories about burning more fat in the morning, prior to food... but like the previous poster said, you might pass out (my wife almost did)... I can work out in the am before eating no problem. When I used to lift weights, I could not do it in the morning. I felt like I was going to die, but I love my morning runs. I am much more flexible in the afternoons, and can run at a much quicker pace. That's just me. I would try both for a week, and see what keeps you more motivated. Good luck!