I get asked this question at least once a week and the response I receive from people is always shock! Many people ask, both men and women, which should they do 1st if they have to fit in both cardio and weights. My answer? STRENGTH. HOWEVER, you can mix up the workout routine and do cardio in between exercises as if you are doing a circuit. This is actually one of my favorites with some of my clients.
Between research and my experience, it's best to perform your resistance workout before you do cardio. Now of course, you should always begin your routine with a proper warm-up of about 5 min followed by CORE exercises. This prepares your body for what you are about to put it through.
Whether you're a first time gym go-er or in the gym every day, form and function is important. Your body is fatigued when cardio is done first. This will not only set you up for bad form, compensations, and possible inury, but also a decrease in max recruitment of your muscles.
So, next time you are in the gym, try this and see if you notice a difference.