We've always had a car, but used the buses a few times we went. The last 3 trips, we've been strictly driving from park to park.
The buses are crowded, you have to wait either at your resort or the part or both for the bus to arrive; then there may be too many people to fit on that bus, so you wait some more. They are loud too, both the engine, and the yelling kids. Most kids are good, so don't flame me on that, but there's plenty that have had a long day and are tired and cry cry cry. Then, you've got your teens that don't know what an indoor voice is either.
My car is always right there ready for me. It's quiet, I also keep a small cooler in it with beverages and maybe a snack.
Getting around WDW is so easy, you cannot get lost.