The Phoenix airport car rental facility is HUGE. It's so huge, that it's not even at the airport. It's a 8-10 min shuttle bus ride away.
It's new and it's clean. Best of all, you can check your luggage in right here and not have to take them with you on the shuttle bus. There are certain restrictions, like you have to do it at least 90 min before your flight and I think only certain airlines offer this service. I know Southwest does.
There are plenty of seats and they even have their own bathrooms. All of the major car rental brands have offices here.
This car rental center has the highest, longest and steepest escalators I've seen. They go up 4 stories, they're continuous and they're steep. If you have luggage, there's a sign that says DO NOT TAKE LUGGAGE ON HERE, USE ELEVATOR INSTEAD. There's probably a good reason for that.
Picking up and dropping off your car is easy and fast. Just pay attention to the freeway signs that will guide you to the center.