There are literally hundreds of threads on this topic. Do a search on MCO rental cars or Port Canaveral rental cars and if you have any new question, come back and ask it.
I've done Budget and Avis and they were basically the same. They have shuttles that pick you up at the port and bring you to the off site location.
Our trip last month we had the rental prior to the cruise for our Universal stay. We just parked it in the garage at the port because we needed to get back to the Swan post cruise.
Cost more but it was nice just walking off the ship and jumping in the car. We were at Epcot by 8:45am.
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