I would always go with the lighter car, as you can add weight if you feel you need it and affect the cog much more with the same weight added. The suspension of a lighter car also works much better because it doesn't have to fight as much inertia, but i agree with you, that heavier vehicles are often easier to drive aggressively. From an engineering standpoint i would say that the lighter car is ALWAYS better, but at the same time you need more self-control to effectively use the benefits of a nimble car (that is not set up perfectly)