I tend to be a cheapskate when renting cars, and consistently rent from Alamo in Maui who has the best pricing when booked through Costco with a suffient lead time.
Some here have had bad experiences with Alamo on Maui but generally I have not. If I have a complaint with them it's there cars typically aren't as clean in Maui as they could be and they hold onto their fleet a bit longer than others. In Maui its as if they ran them through the car wash but didn't spend much time detailing them once they come out as others do. I usually book through Costco because they include a second driver for no extra cost and usually have the best price. Nationwide this year I've rented from Alamo, Budget, Dollar and in about a week, Avis.
Phil is correct that Priceline and Hotwire are your best bet for last minute rentals.