It depends on all of that, Georgianne, as well as what color shirt you're wearing and your middle name.

It's crazy... I've just been going through the same thing. Had a ressie with
Avis, because I'll be at the Radisson anyway, but several people suggested Budget. I used the
Walmart code, and it was way cheaper (compact car for just DS and I) than Avis. Then I noticed a thing on the Discover card site when I was paying my bill about Budget -- clicked through and got the same great rate as the Walmart code, plus was able to print out a coupon for $10 off any two-day rental (I assume that means at least two days; my rental is for two days exactly anyway.) I just have to pay with my Discover card, which I was going to do anyway.

Brought my total rental cost down to an awesome $44.50.
I also had received some discounts for Avis via my Sears card, but couldn't use any of them as they all were quite restrictive. You might want to check with any credit card companies you deal with, check out their web pages, and see what car rental deals you can get if you use that particular card!
-gina-