I do mine after for maximum fat loss... low-intensity right after workout...My personal belief based on experience is that doing cardio after a workout is the best way to achieve highest levels of fat burning.
I like first thing in the morning on an empty stomach -- glycogen levels are extremely low due to fast while sleeping. If that is not an option, then do your cardio after training. You will have used up a significant amount of your bodies carb storage and can quickly move into the "fat burning" mode.
Be careful with the intensity levels. To high of an intensity level eaither post workout or pre breakfast can result in burning more muscle than necessary.
sometimes I used to run/jog 10 - 15 minutes before my workouts - i liked this because it warmed me up before lifting. Then I started to run/jog after workouts because i heard this was better (20 minutes). I didn't really see dramatic results either way. Within the last month, I started using the FAT BURNING option on the treadmill. i walk around 4 - 4.5mph (20 minutes after workout) while holding onto the sensors and the treadmill automatically adjusts to keep my heart rate in the target fat burning zone. Since then I trimmed up incredibly. That's all i gotta say about that.
I rarely do cardio, as I allow my diet and workouts to reduce my bodyfat. But when I do add cardio to remove the last couple of pounds, I opt for cardio immediately following my weight workout in the evening.