Great question! I was just going to ask this exact question this morning.

Me, I enjoy running in the mornings. I have a lot more energy and strength in the morning than I do later in the day. Sure, evenings were convenient; I was free to run whenever and didn't have to wake up early, but I realized how great morning runs are for me. It's much cooler (and tolerable) in the summer months and because my stomach hasn't eaten a big meal, it doesn't get upset during my run.