Based on the principles of specificity, I would recommend cardio post workout to elicit the best results in strength training and muscle building.
However, if your main goal is to run a marathon or train for an endurance sport/competition, then, cardio should be applied before and/or after a workout. Clearly there will always be a debate as to whether cardio should be done before or after a resistance training session, but, in my opinion, it all comes down to specificity and what your goals are and at what level of intensity you are doing the cardio. If you are interested in getting a free first workout and evaluation simply click here to register and book online