Do what feels good for you and works with your schedule. Remember the only rule to running is to be sure you get your shoes properly fitted and to just go out and do it. The rest is up to you! I prefer a.m. in the summer to avoid the heat and humidity. I love nighttime running in the fall/winter and just really can't live without my Saturday a.m. long runs.
For me, it depends on season, day of the week, and geographic location.
In the summer, I will run late in the evening if I'm home in the city... if I'm at the beach, then I find myself getting up early and always hit the boardwalk before it heats up and gets crowded.
Now that it's fall, if I get the chance to shoot down to the beach, I'll run whenever I can get there... if I'm home, I run late afternoon/early evenings during the week and late mornings on the weekends. Same pretty much goes for the spring.
Winter, I hibernate... so getting me out at all is nothing short of a miracle.
I like mornings in the summer to try to beat the heat, but the downside is the humidity is sometimes worse. Mornings in the fall, because I have more daylight. During the depths of winter I've been lucky to work from home so I can go at lunch in the "warmest" part of the day. In the spring, I like running in the evening.
Very much an evening person, favourite time to run is 8-10pm. I struggle enough with getting up for early classes without trying to get up even earlier to run.
My couch - 15 Jul 2008
Dublin Marathon - 26 October 2009
Personally I prefer mornings. I like to see the sun come up as I run and it brings back a little nostalgia for the military life (can't believe I think that now ). Also, I live near an interstate--Ozone levels are lower in the morning so it is not as hard on the lungs. That said, I have often heard taht evening runs are better because you are loosened up and can train harder. So sometimes I run in the afternoon. Sometimes I run both morning and afternoon.
I rather run in the evenings, as its difficult to get up early in the morning, plus I have limited time in the mornings before work, so its better in the evenings when I can eat something before and be more relaxed.