Hi Candy,
Our experience has always been to rely on Disney transportation. We know that sometimes this means waiting and also standing on buses, but we like the simplicity of relying on someone else to do the driving. We don't have to worry about reading signs/maps or buckling into car seats (that was a few years ago, though!). If we park hop, we don't need to worry about returning to the first park to get a car later in the evening. Disney transportation has always gotten us where we wanted to go in a timely manner, and its FREE!
However, I know many other guests are just as adamant about renting a car. Cars can be rented at the airport or at Walt Disney World. They like the control of their own time and being able to park right next to the building they are staying at. Since you are a Disney resort guest, parking will be free at the parks.
I thought I'd throw out a couple of thoughts on transportation to help you see some more opinions:
here,
here, and
here.
It truly comes down to a personal preference for your family, but I'm hoping that once you read more of the pros and cons, you'll be able to make a more informed decision
Thank you for the question; please let us know if we can help again.