Make your choice depending on your itinerary and budget; not based on worry about getting lost on the way to the port.

I was really stressed about it, and it was really very simple.
We did the rental car for the trip in, and transfers for the day we left, which was the easiest for our plans (although not the best for the budget because Disney transfers are definately more expensive.)
We rented on the way in because we were arriving a couple days early and wanted to have a car to go to Cape Canaveral etc before the cruise. I got the ressie on the internet after checking sites, using codes etc. We had never traveled out of the Orlando airport on our own, and have never been to the port. I was anxious because we were supposed to arrive at 6pm which would give us plenty of daylight, but had to switch to a later flight out, so we arrived around 10pm. It was no problem. I had printed directions from mapquest from the airport to Ron Jons, and also got detailed directions from the Budget personnel just in case. We had an easy, traffic free ride to to hotel near the port.
We dropped the car at the Budget site near Ron Jons Sat. am and had no problem getting a shuttle (just us and our luggage) over to the port, with the only cost being a tip for the driver.
On the way home we decided to take the Disney transfer because we were going right to the day room at the airport to rest until our late flight out. It was extremely easy, and for this convenience I was willing to pay the extra dollars.