Here is what me and my wife did, which I think was the best thing.
Do not Reserve rental ahead of time. Big Mistake.
When we arrived in Aruba, we crossed the road and stopped by at every car rental place. Asked for the price, asked if they accepted AmEx (my insurance was with AmEx), lowest price for the Jeep that we got for auto was $325 for a week w/liability insurance, however, since they didn't accept AmEx, we went to the next one, prices varied from $325 to $380. When rental reps saw us walking from one to another, they all were calling to come in because they had a deal for us, we ended up at Royal rental, they had Ford Sport Trak auto 4x4 for $350, bigger car with ac and a real gas guzzler, pricewise I thought it was pretty reasonable, so we went with them. Royal was our choice for the second time. They have reasonable prices and reasonable cars. So go out there and make them come to you and offer you a deal.