I am with the others. The best time is the one you can make available. That said, it would be great if you could have eaten a little bit before to give yourself some energy to exercise.
I must confess, though, that I worked out for many years at 5:30 in the morning without having eaten anything at all. I am not a morning person but it was the only time when I still had control over my day before going to my corporate job.