For me personally I find its best in the morning.
It wakes me up and gets me going for the day. Seriously the state I walk into the gym in the mornings is just shocking!!I literally roll out of bed into my clothes and shoes. Pull my hair out of my face and sometimes if I am awake enough I will brush my teeth and wash my face. If not, I dont!

But after I have wroked out I feel awake refreshed and ready to face the day. So I get home and if the kids are up then I will start the breakfast if they arent I will jump in the shower. Its done and dusted and the rest of the day is mine.
If DH is on dayshifts then I cant go in the morning and by the time he gets home it really is a struggle to get out door. My motivation just isnt there and I want nothing more than to relax and hand the kids over. Not go sweat my ar$e off. I also find I start dreading it knowing that I am going to have to go soon.

So I vote for mornings