I don't have the least, every hour is precious.
But the most fav is when all of my team leave the office (8pm). I sit alone to get things done and still get the office atmosphere to do the work.
My least favorite hour to work is right after lunch because I often feel sluggish and less productive. However, my most favorite time is early in the morning, as the quiet and fresh start to the day boosts my creativity and focus.