I've gotten Alamo and National. National was great. Alamo was terrible. Their pushy salespeople and their location just make the whole thing so stressful. I won't use Priceline anymore because I am afraid of getting Alamo. I got great codes at mousesavers. Minivan at Dollar in peak summer season for $209 per week. I know I would not get it that cheap at priceline, as I've tried. I get the message that says that my bid is below a level for a slim chance of getting a car. The Dollar codes that worked best for me were MCC and FISH. I was looking for a minivan. You may want to try the others for a different type of car.
Good luck.