We were in Phoenix on a golfing vacation. I was surprised that the rental car place wasn't attached to the airport, but there is a free shuttle service to and from the airport. We arrived mid-day and got to the rental car plaza. The wait was a bit long here, but once you sign your papers and get your keys its not too bad. You have to head downstairs to the parking garage and pick up your rental.
We ended up with a grandpa car (buick), but its fine because the trunk was big enough for 2 golf bags and a large suitcase. The car overall was clean and ran fine.
When returning the process was also very easy and pretty fast. Just pull into the garage and wait for someone to check you in. The location is pretty easy to find off the express way- there are tons of signs clearly marking where you need to go.