If we fly, we always rent a car. It is more expensive, and it's probably not a necessity, but my family prefers the freedom of having a car. We like driving ourselves to and from the parks. Sometimes the buses are faster than driving and walking/tramming in from the parking lot, but often there are waits for buses and you save time by driving. If we want to go off-property for something, we can easily do so. I feel a little out of control if I don't have my own transportation. It's hard to say how much time we save by driving instead of relying on Disney transportation, but having a car is well worth it to us.