Hertz will not allow you to rent even when you are an AAA member.
Matter of fact, they mailed me that big Gold membership thing from them, with a ton of coupons..but as I am under 25 I will not be able to use them.
Enterprise is your best bet, Alamo is after this the secondnicest one, Budget can be accomdating at times.
Sometimes Priceline helps you.
Besides this: Bad luck, we just have to swallow this.
My brother in Germany had an AVIS business account, he was 18, but because it was booked over his business thing, they gave him a car (brandnew Golf Convertable with 230 miles on it) without any extra charge.