1. Weight training and Cardio on seperate days. Best option.
2. Cardio straight after weight training, incase the Cardio uses up significant amounts of Glucose, Glycogen and ATP, affecting weights workouts. Second best.
3. Weights in the morning, Cardio in the evening. As long as you're well fed and rested in the interim hours, it should be okay, taking care not to do substantial Cardio, I.E. 1hr steady state, versus 20-30 minutes interval training.
4. Cardio first, weights afterwards. Some say it makes a difference to weights some say not. Two factors include the intensity and duration of Cardio and the intensity and duration of weights, so it's whether you try it and struggle a bit on the weights. If not and you feel okay doing them that way round fine, otherwise do them the Cardio afterwards, later on, or on non-weights days.