Is strength training or cardio training more effective for weight loss?

Both are the most effective.  You can't have one without the other.  Each one of these has its own benefits.  Weight training will help increase your BMR(Basal Metoblic Rate) which in turn helps you burn more calories to lose weight.  Also cardio helps burn more calories quicker than just weight training alone and helps increase your endurance, lower blood pressure and resting heart rate.  Also you can combine the two if you are short on time for workouts.  Just remember to lose weight it is all a numbers game.  You have to burn more calories than you take in.