I do my initial check at www.kayak.com so I have a basis for the car types I'm looking for. Then I check www.hotwire.com knowing that I won't know the car company, but I will have another idea on prices. Then I try the mousesavers car rental IDs and coupons.
I booked a full size car with Alamo for 10 days starting next week. I joined their *********** club, searched for a promotion code online and got an additional $35 off with a code from retailmenot.com. The price would have been $356 but I got it for $192 after discounts. Then I jumped and said yipee.
The best advice you can get is to book the best no cancellation fee rate you can find today. Keep checking rates and as you see better ones, book them and then cancel the older more expensive rate. We do this all the time with Alamo and many times it has saved us money both ways. Because the prices went up and we were happy we booked early, and also because the prices went down and we were able to book the lower rate and cancel the higher.
I love mousesavers, but I couldn't find a good minivan deal with any of their codes for December. I went to carrentalsavers.com, got a code for Budget not listed on mousesavers and used the $30 off Costco coupon (total $295-$30 coupon). They list all the car companies so that you can see the prices and if you click on the change search options button you can see all the codes they use to get the prices. Supposedly they list the codes that give the best discount that anyone can use. You need to go to the Florida search though, not the general one. If you need help because this didn't make sense, send me a pm!