For me it's a few hours after work. I normally come home, relax for a bit, eat, then workout. I can't do it in the early morning because I never feel like I have much energy in the morning. And I don't do it before work period because I feel like I don't have as much mental focus knowing I have to go to work after, it just kills the high for me.
I feel you on the morning part. I've tried everything to motivate myself to work out in the morning. It doesn't matter if I get 4 hours of sleep or 10, my mind is just not mentally ready to do a workout. When I did it, it never felt like it went as good as it does now.
That said, I'm completely the opposite about the mental focus at work. I LOVE working out at lunch because I feel sooo much more confident when I come back. My endorphins are going, and I still have that "pump" feeling. I actually request all my meets with vendors to be in the afternoon, because I feel so much more confident during the meetings.