I like to exercise in the morning and the evening. I do power walking/jogging for 30-40 minutes around an hour or two after breakfast (don't want to get cramps!) as that's when I feel like I have the most energy. And later in the evening, say around 6 or 7, I'll go for a 40-50 minute power walk/jog. Best of both worlds, I say.
Although, if I had to choose a preferred time to exercise, it would be in the morning. You get it over with, which is a great feeling and it jump starts your day.