No problems here! This is the second company we try in this lobby full of car rental companies. Avis is just a 10 to 15 minute bus ride from the Phoenix airports via car rental shuttle. Signs in the airport are clearly marked to reach the shuttle area :-)
Due to the busy holidays they didn't have any economy-sized cars left so we had to go with a CRV type vehicle. The car was nice and clean and well maintained considering it had almost 18,000 miles.
Check out was pretty painless too. I rated this 4 and not 5 stars just because of the steep price. We only rented this car for about 5 hours and the price is just too steep considering how long we rented.
Sometimes the shuttle back to the terminal can take a few minutes so be sure to plan accordingly. Also if you have a pet there's a gravel area on the ground floor where you can try taking them as long as you pick up after them. When you're outside it's just to the right and you basically go down all the stairs and to your right. The gravel stretches pretty far along the car return area :-)