As the link says, AAA often gets you good rates. You also can save around 30% by prepaying, but the catch is that there is absolutely no changing the reservation. So you have to be sure you want exactly what and when you reserved.
I find that half the time when I reserve an economy car, they try to fob me off with an "upgrade" to midsize. My rental car has to fit through a very narrow gate where I'm going, so I need the economy car. I have to say even the economy cars aren't exactly tiny. But at peak times, the chances you'll be "upgraded" while paying the price of the smallest car are significant.