We rented a car (a minivan actually) on our last trip and we're doing it again this time. Personally, we prefer the freedom of having our own transportation. We can come & go as we please on our schedule, which is important since we have small kids. We are able to leave resort property to go to WalMart or wherever to stock up on things like PB&J, cereal, milk, etc, to keep in the room.
This is how we did it: We mapquested. Every single place where we thought we might go, we mapquested at home. From the rental place, to POP, to all the area sights (other than Disney, of course), we mapquested, and then kept everything in a folder. We were picked up at the airport by the car rental shuttle (very easy to find, btw, we just asked airport personnel where to go and they directed us with no problem), we were shuttled right to the door, picked up our minivan, and were on our way. There was one instance where I forgot the maps, thought I'd remember my way to & from WalMart. Well, I got lost. It was getting dark, and so I called my husband, panicking, and he went to the front desk at POP, and got a CM on the phone, who very calmly and efficiently directed me right back to the resort.
When we were leaving, we pulled up and in, literally got out of the minivan and onto another shuttle where we were dropped off at MCO. Very easy to manage.
The main things to remember are that you have to pay tolls to and from the airport, and make sure to fill up the gas tank prior to drop-off somewhere a bit further away from the airport (prices were significantly higher the closer we got to MCO.
The convenience of having transportation far outweighed any minor issues.