The last rental, at IAD, involved a car that kept shuddering when at speeds over 40 mph and would slip into a lower gear and throw the rider forward while driving. I called Hertz immediately and they wouldn't come to where I was and trade out cars, they would only exchange the unsafe vehicle at IAD. I wasn't comfortable driving in the car in DC traffic with it cutting out and virtually dropping 30 mph in a second. After multiple discussions with Hertz, where they were apathetic at best and rude in some cases, I was able to drop the car off at a dealership with a Hertz desk where they gave me a car with an eighth of a tank of gas, said in the contract it was a half a tank and then told me that they couldn't change the contract but that they would put in a note that it was ok for me to drop off the car at IAD with an eighth of a tank. How do you fill a tank with an eighth of a tank of gas when you return it? In SAC, I got a car with a low brake fluid light and they said it was ok to drive, they didn't think it would be a problem and there weren't any other cars available. I have been stranded at airports with no car because my flight was late and they gave away all their cars. I had to take a cab and they didn't reimburse me for the taxis or find me a car at some point during the trip. Ive had very smoky or dirty interiors. Out of the past 12 rentals, I've had problems with 10 of them. I don't ask for much and I don't pull the DYKWIA act or anything. I just want the car I reserved available when I arrive. I like having my name on the board and getting to skip the lines and go straight to the car, but I realize that at small airports, this won't happen. And I'd like to know that when I reserve an intermediate or compact car, I get that car, even if my flight is delayed. I think the benefits of a frequent renter I would like the best are: skipping check in lines, expedited check in and check out, an easier reservation process with my information filled in once I sign in as a "premier". The only other additional nice to have would be the ability to upgrade.