I rent frequently and always from Avis. I can't be bothered to go into the rental counter when I pick up my car. At my first FlyerTalk event I got a great tip from mweiss if I remember correctly. Since I always use my corporate AMEX, I just periodically send in the little receipts that come with the bill (I sent in 20 at one time once) to the airline and request credit. I did this with AS and they credited them within a couple of weeks. Ya gotta love this place.