WHICHEVER APPLIES TO YOUR GOALS.
For example, the only time I would consider cardio for the bulk of my workout would be if I were training for a marathon of some sort. You want to tackle the exercise that prepares you for your goals first, when your body is fresh.
Since strength training is the focus for all my long term goals of being fit and healthy, I prefer to save my energy for that part of my workout. I use what energy I have left after I lift and put it into my cardio. I don't like being tired from cardio when I am trying to lift heavy things. Your form will suffer and will lead to injuries.
ALSO, you won't be able to lift as much weight when you are tired. So I lift first when I'm fresh and whatever is left in me I give to cardio…even if I only have 10 mins left in my workout. Strength training is the important part of my workout.
And when I say, "won't be able to lift as much" Should you lift heavy or light weights? Post to come….