I typically use Alamo when I come to Vegas, but since joining the Emerald Club earlier this year I've been using National exclusively.
As you well know, Emerald Club members can skip the counter and choose any car in the Emerald Aisle. Unfortunately, at 6:00pm on a Saturday night, said Aisle was looking a little spartan. Most cars there are at least in the Standard class, but that night it was mostly filled with crappy Dodge Avengers and Chevy Impalas.
I was gonna take a black Impala but some other people beat me to it. There was a white one next to it so I ended up taking that one. It was a fully loaded model with leather, sunroof, remote start and working XM radio. Even though it's a pretty plain car, it was pretty comfortable. It's classified as a full-size car and I paid the intermediate rate of like $20 a day.
Returning was pretty easy. They scan the barcode, punch in the mileage and make sure the gas is full. I get the receipts emailed to me so I didn't even have to wait for one to print out.
National/Alamo make the car rental process so easy...you'd be a fool not to use them.