I guess we all have different experiences. You can put in a preference in your profile. Consequently, I routinely get a Grand Marquis or Towncar. Last week I got a Cadillac Escalade. This week, I got a Towncar and upgraded for $20/day to a Navigator.
For me the PC has been a huge benefit at only $250 I am extremely happy.
Now, a few out of the way locations required me to school them on the benefits. Once, a new person at the Orange county airport tried to convince me that the upgrade was space available. I had him check with his manager who corrected him and I got a better upgrade.
Similarly at the Detroit airport, they didn't upgrade me, citing that they didn't have any premium cars. Once again I had them check with their manager who did some research and learned that it was guaranteed upgrade. I got a large SUV as a result.
I find that the guaranteed upgrade and guaranteed availability are particularly useful when traveling during the holiday weekend.
Last Christmas the LAX location was sold out. Every company which had availability wanted like $130 for a Ford Taurus. My PC had expired but I got it reinstated that day. I was able to rent a full sized car for $60, which was automatically upgraded to a Town car.
Like I said, my experiences have been very good with PC