answer:Why not a combination of both? I am a fierce believer of circuit work out. I do a routine called the 300. 6 exercises, 50 reps each – within 30 minutes. Do that today and let me know if you don’t get wiped out. Generally, from all the one on one sessions with a personal trainer – they stress do one or the other not both. My own workout regiment is this: MWF workout (circuit) T Th run on a treadmill. Good to let your body rest between anaerobic exercise. This is assuming you go 5 days a week. You are going 5 days a week right? :P Have a good workout.