What's the best cardio exercise for quick weight loss?

For quick weight loss you need to be raising your resting metabolic rate at the same time as burning as much energy as possible during the workout itself. For this I recommend a high intensity, full body workout, like burpees or boxing circuits. Keep the workouts short - less than half an hour - but intense with minimal rests. This way you'll raise your resting metabolic rate, meaning that you'll continue to burn energy at a higher rate than usual for anything up to 24 hours after your workout has actually finished. Short, high intensity exercise kills your appetite as well, which will help your weight loss goals. Steady state cardio for hours on end, although it may burn more calories during the workout itself, doesn't have the same metabolic effect that high intensity exercise does, and it also makes you damn hungry.