So how would we like ours served up? With cloth cap or a metal helmet? An article of faith that divides the open-top fraternity when they contemplate the choice between different models such as the BMW 3 or Audi A5. And now they have the same decision to make with one and the same vehicle. The retractable roof of the Mazda MX-5 Roadster Coupe is quieter and more weatherproof, plus it can be closed or opened by the simple press of a button. Or at least according to its advocates. But purists will turn up their noses. A real roadster has a manually operated fabric roof and nothing else. A genuine roadster driver is made of sterner stuff. And in any case, it looks flashier.