I suggest that strength training be done when strength is available. After cardiorespiratory training the muscular strength has been degraded. However, after a strength training session, you can still raise and lower your heart rate just as effectively as if you were doing it before. The pace will be a bit slower but with the same results, is that really a bad thing? However, if cardio IS your goal, then cardio should be done first. Its all about what you want to enhance the most getting the priority in your workouts.