I've often wondered - what features does a car need to have to make it a 'Premium' class model, rather than an F or YF? I mean, a fully loaded Impala classed as YF, with leather, Sirius, sunroof, electric seats etc. is probably more 'premium' that a basic spec Maxima isn't it?

So are there any specific features that Hertz use to determine what is Premium and what isn't? Bigger engines? Bigger trunk? Leather? I'm going to book a Premium for our trip to Chicago next year, as we'll be covering about 2500miles in 2 weeks, so I'm hoping for something that is a bit more comfortable than the usual full size we normally rent, but I really don't know what will be different about it!