Just tell them, whoever you come in contact with. Your preferences will be noted. Soon you'll be getting put in a Fiat 500, Volvo C30, or Mazda 2.
There are others you may like. So study the
http://www.flyertalk.com/forum/hertz...t-you-get.html and familiarize yourself with the models.
Hertz Gold agents who pre-assign vehicles do check customer notes, and many take great pride in learning favorite models of customers. It is very helpful to them if you can identify a specific model as your favorite.
I like the Toyota Corolla myself. It is my current favorite in the fleet, for all the reasons you mentioned.