They are mostly the same. Non of the rental companies have a drop off point at the cruise terminal. You will have to pass the ship and go into Coca Beach to drop of the car for most of the rental companies. BUT, the major companies will shuttle you to/from the ship too as their business is pretty much made up of cruisers doing this.
We used AVIS and they were reasonable. Your real question should be, which rental companies have pick up points inside MCO? Avis and Hertz are right there across the street from the luggage pickup, Some of the other companies require you to take a shuttle bus outside the airport to pick up your car. Not a big deal, but with lots of luggage, maybe a bigger hassle.
I know Avis and Hertz do this, the others you will have to call and ask.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007