Depends on the airport, but Dollar generally are using Liberty's for standard/intermediate SUV, and the Cherokee Laredo for the full size.
Be aware that they do have some Kia Sorento's for full-size at MCO. If you're after a specific vehicle, just ask when you reserve and they'll note it. remember it's not guaranteed, but it does improve your chances of getting what you want.
I'm upgrading to a Premium, so it's similar in cost to the SUV's, but with a Chrysler Pacifica... bigger, more luxurious, but not in the SUV category....