Love that you can rent a car from a machine and skip the line. You also don't get the pushy sales rep trying to upsell you a full tank of gas or upgrades when you use the self service machines. They do let you pick your own car within the category (standard, full size, SUV, etc.) you've selected. You basically take your receipt to the garage and pick your car. Key's are already in the car. Drive to the exit, show them your ID and receipt and you are on your way.
Returns are just as easy. I've rented from other companies before and it's a pain. Long waits and slow service. Firefly is on my mind when I say this.
I come to Vegas often and only rent from Alamo. Never had a problem.