I've always used Dollar, hired a car at LAX on one trip and got a slow puncture in JTree, drove to Palm Springs to drop a friend off and thought I'd pop in to the Dollar branch in Palm Springs and get them to change it...they took the car and upgraded me to a different one and sent me on my way!
As a contrast I once hired a car via enterprise in the U.K. and got a puncture (nail in tyre). Called Enterprise who told me to get it replaced otherwise they'd do it and charge me more than it would cost me at a local garage!!