I've worked out in the morning, at lunch times and in the evenings and find all very beneficial in their own way. Working out in the morning though didn't necessarily mean I had woken enough and had enough energy to do a hard workout. Working in the evening I was sometimes too tired and this impacted on my level of strength and stamina. Working out at lunch time always seemed to be best fitted for me and my lifestyle, but I missed getting outside so much at lunchtime and away from the office, and I like the sun*!
*fresh air, I live in the UK so sun isn't always at it's optimum!