Convenience has won my heart and Yelp stars. =)
The bus from the airport to the central hub is available non-stop. The fact that the majority of rental agencies are located in ONE building amazes me. Picking up and dropping off your rental is easy. There is always someone downstairs to greet you, check you in, and print out your receipt.
Squeaky clean establishment and the lines at each of the counters are never too long. I'm always a happy camper when I visit Vegas.