Recent research has shown that training after work can result in a less effective session since you may already be mentally fatigued, but in the end it really comes down to your schedule.
What's the best time of day for you to train? Read: The time of day that you will actually train, and not just go through the motions. If you're not a morning person and you force yourself to train at 6 am, you probably won't be very consistent, nor will you train to your potential. If it seems like there's never a good time, then try to find ways to work activity into your day in short spurts, even if it's finding time to do some bodyweight exercise in the morning, a little aerobic activity in the afternoon, and stretching at night.
Rather than waiting for the perfect opportunity to exercise, make movement part of your daily life.
--Nick Anthony, performance specialist, Athletes' Performance