I don't have an absolute favorite per se. However I have had good experiences with Dollar, National and Avis. All are located on the airport at Orlando and make getting your car a breeze. For me, between those three, I would take the one with the best deal for your dates.
National is my Fav. But I agree with previouse post, any of the 3 that are right at the airport. I have used all and will use the one with the best price.