As noted above, there seems to be a lot of evidence that points towards morning workouts being ideal. The studies have found that those who workout in the am have better energy all day, maximizing the benefit of their workout.
Still, I love to workout early evening - after work or around 7pm. I love the feeling of working out, coming home for a hot shower and puttin on my PJs. I think I am used to this though, as it has been my routine for over three years now! On the weekends, I prefer to head into the gym earlier - between 9:30 and 11am.
Really, the best time to workout is the time that accommodates your schedule best. While working out in the morning would be great, I don't think anyone is going to blame you for not wanting to get up at 6am and head to the gym!