LAS is a Hertz location that offers "Ultimate Choice" service; suggest you review the FAQ in the wikipost of the following thread to familiarize yourself to this service. Questions/Discussion About Hertz Ultimate Choice Service

When using Ultimate Choice, I seek vehicles in a certain bodystyle (SUV vs. sedan or coupe), then trim package (I look for higher trim levels for the added features), functional Sirius/XM satellite radio, and low mileage. That being said, I do not think the selection of cars in the Gold Member section will be that varied when compared to that of the sections reserved for renters with elite status in Hertz' frequent renter program. Consolidated "Renting at LAS; What Kind of Cars to Expect?" Thread

Echoing the advise given to you in the Avis forum; a sedan vs. an SUV is a subjective decision for you to make; given the amount of distance you will be covering, the better fuel efficiency of a sedan may be attractive; the additional storage and higher driving stance of an SUV may offset the additional petrol costs.