In a race application, I would use an aluminum flywheel. It lets the motor rev a lot quicker through the powerband up to the shift point. In a very indirect way, it almost acts like a steeper gear. In a slower street car, heavy car, or something not making "that much" power, it's still debated whether aluminum is better than steel. As we know, steel would have more stored energy than the aluminum because it's heavier. Steel is much more smooth while the clutch is engaging compared to aluminum. The question is whether the aluminum can shock the tires as hard as a steel flywheel could. I don't see how it could, but it is still debated.
Joe