around here, you need atleast 1kwatts to get anyone attention. i toyed with an ID12v3 and great sub nice and clean. as for the hertz.. i have no experience.
Both look like they would get the job done. The ID12 is a very clean sounding sub but doesnt have much SPL kick. Ive never heard that model of the Hertz but im sure it would be about the same. Since you already have something Hertz in your car you might as well match it with the substage.