What I have come to realize after working out in the entire spectrum of times is that consistency plays the largest role.
When I was a dumb 14 year old I used to lift at 1 am before bed during the summer
When I hit HS it was 2:00 every day after school
When I went to college it became 5 pm everyday
During winter break I go in at about noon
In the summers I get up before work (6am) to go to the gym because I life guard and all the sun ruins me for an after work workout.
The most important part about finding the right time is going at that time consistently. The first week of adjusting to a new time can be tough, but after a few days your body gets used to it and you'll perform just as well as you did when you went at your previous time. If your not a morning person, working out in the AM can make you a morning person, after the initial shock of your first few workouts.
I realize I am missing the question of when the BEST time is to workout, just thought it should be mentioned that anytime can be a good time to workout, provided you don't do anything screwy with your nutrition.