My experience at the Car Rental Center at PHX wasn't as bad as some made it seem. Getting here wasn't a problem so long as you're able to read and follow basic directions. Get off your flight, follow the signs to the shuttle and get to the appropriate counter to start/finish your rental.
The shuttle ride is about 15 minutes from the airport to the off site rental building and buses leave on a continuous time schedule. Conveniently all the rental companies operate out of one building so there's no need to go anywhere else. Its a point A to B sort of thing.
The rental building itself is large and could definitely accommodate large crowds although when i was there it was dead.
The pick up/return areas are well signed so you know where to leave the vehicle upon return and where to head to when picking up.
If you need to get to south Arizona by air and need to rent a car I'd suggest you give this place a go! I'd use it again.