Comparing car rental rates ensures that you're getting the best prices available. I don't believe that there is one cheapest car rental company or one best company. I think the better company is the one that gives you what YOU want at a great price. Costs will depend on the particulars of your rental: Locations, Dates & Times and Vehicle Size.
The company that gave you the best car rental rate for your trip last year, may not necessarily be the cheapest provider for that trip you've planned next month. You need to compare vehicles and rates to make sure that you always get the greatest offer!
I believe that doing some research and booking in advance will give you the best possible price.
An easy way of comparing car rental rates is to use a booking site to check different company's rates. Then try the specific company's website to see if you can get the rental car rate even cheaper by using a discount code. There are hundreds of membership programs and professional associations that offer discount codes to their members.
Comparing Car Rental Rates Test
Always compare bottom line prices including taxes.. and remember, although I didn't check any optional purchases here, if you're going to be looking at insurance, car seats, additional drivers, etc. those prices vary ... include them in your bottom line when you compare rental cars and companies!
I checked on a major booking site for a midsize car at Newark, New Jersey Airport (EWR) for a 7 day rental in early December. Comparing rates between 6 national car rental companies, I found the following ( links open in a new window):
Let's say I have a membership with Allstate Motor Club. I went back to each car rental company's website and checked the rates using a car rental discount code for Allstate Motor Club members with Enterprise, Avis, National, Budget and Hertz. The savings were (at the time that I checked - remember rates change all the time!):
The Enterprise rate went down to $315.19 (a savings of about 4%)
The Avis rate went down to $475.99 (a savings of about 9%).
The National rate remained unchanged.
The Budget rate went down to $520.43 (a savings of about 10.9%)
The Hertz rate went down to $432.47 (a savings of about 27%)
It just goes to show that doing a little research and comparing car rental rates can add up to big savings on your next car rental. Always try to use a discount code if you have one, and book in advance to take advantage of the best prices and possible advance booking offers.