well for sure at STI you have a LOT of choices. there is a row of at least 5 or more larger car rental companies inthe airport itself! Actually you have to come out of the airport to access their rooms! Then there are probably another 5 or 6 companies within walking distance. Which even if it was less than 1/4 mile would be a pain with luggage! But with the search button, maybe you will find a few threads that can come up with some recomendations and phone numbers. I bet the ones not right at the airport, but just down the road a few hundred yards would meet you at the terminal exits. I have only rented with one company and for a first timer, i dont think i would recomend them. After a few trips , maybe they could be of some benefit. But for the first time, you want it to go as sloothly as possible, even if it costs you a little more money!
read up on the insurance issues as well... and what people have said about potential liabilities and how they relate to a foreigner renting a car here.
good luck
bob