Short answer: It depends on your fitness goals.
If you want to lose fat, the cardio option is a good way to start. After the cardio depletes your body's energy from its supply of glycogen (stored in the muscles), it turns to its longer-term energy storage source—fat.
If your goal is to build muscle, it's better to hit the weights first. Since cardio induces fatigue, hopping on the treadmill first thing could compromise your form and technique when performing lifting movements.
However, you'd actually be best served to break up the two workouts into separate days rather than performing them one right after the other.
Performing cardio and resistance training on the same day has been found to limit muscle gain, for example.