Does Hertz have a desk at the station? If so, can you skip the queue if you are a Hertz Club member?
The car rental offices at the Avignon TGV Station are quite small....in my experience, queues are rare.
There was a considerable queue when we picked up from Avis on a Saturday afternoon in mid-May 2011. It took about 30 minutes to get the car, but I don't know if this is typical.