well, just to balance this thread--we always rent a car, and wouldn't do it any other way. We live in a fairly small town and do not spend hours in our car commuting while at home, so have no need to "escape" that. (My dh rides his bike to work every day.) We don't care to wait for buses. Vacation is too short to stand around and wait for a bus that may or may not have a seat for us. I do have to say, though, it would be nice to meet more people while there, so if the bus helps you do that, that is nice.
We dine at other resorts frequently, and going resort to resort is long and time consuming on the buses. If you didn't do this as often as we do, you would have less need for a car. We don't want to take a taxi to go to dinner every night either. If you will mainly be spending your time in the parks, you will have less need for a car than we do.
We always go off property at least once to Seaworld, so that also factors in to our decision. We like the idea that we are "masters of our own fate"--that we can go,--or not go--anywhere we want at anytime. If there was any kind of emergency, we would have access to a car immediately.
Where you stay on property also might persuade you. I have heard some resorts have longer commute time.
Picking up and returning rental cars has never been a hassle for us. Neither is parking--at resorts we valet. (free all day at all resorts after paying once at any resort)
So, my advice for people is: if you will be going to other resorts a lot, or off property at all and you are the type who likes to be in charge of your own fate (car is always ready to go, and very comfortable) then you should rent. If you don 't mind taking buses and will only be going to the parks, and you are staying in a very convenient resort, the buses might be fun for you.
No matter what you decide, hope you have a great time!