Which is best? Can't tell if they all offer unlimited mileage
When you get an online rate quote, it will either show "Unlimited Miles" or a per-mile rate (in addition to the daily/weekly rate), such as "0.27 per mile."
The only time I see per-mile rates is on some one-way (different rental and return location) rentals, and, even then, this is rare in Florida.
As far as the best company, the major brands are all similar. I happen to like National these days, after being loyal to Hertz for a long time. Price can be a key difference.
Probably the most important factor is having a good contract I.D. code and/or coupon code. Start by seeing if your employer has a relationship with a preferred rental car provider and if that relationship allows the contract I.D. code to be used for non-business rentals. There are a myriad of other places to get codes, including
AAA, Costco, labor unions, frequent flyer programs, travel providers, and many websites. Some codes are much better than others. Often you can combine a contract code with a coupon code.
At Orlando International, the following companies are in the airport, with no need to take a shuttle to an off-airport location:
Advantage Rent A Car
Alamo
Avis
Budget
Dollar Car Rental
Enterprise Rent-A-Car
E-Z Rent A Car
Hertz Car Rental
L and M Car Rental
National
Thrifty
Advantage (the leisure part of Hertz) often has good rates. If you're a AAA member and you enter your AAA chapter code during the online reservation process, you might get an even better rate.
Also, see if you qualify for free membership in a program such as National's Emerald Club or Hertz's Number One Gold. These programs are meant for frequent business renters, but there's no reason not to sign up even if you only rent cars once or twice a year. Such programs speed up the rental process by letting you bypass the counter.