I guess it all depends on what you like. The bus service at AKL is perhaps the best in the park. If you find driving stressful or bothersome, the busses are the way to go. It will take a bit longer than driving (at least in our experience, note we have no kids, so no carseat concerns), but you will probably be more relaxed.
Personally, I prefer to drive. I dont like waiting for busses and I am not real comfortable riding in them. I am much more relaxed when I do the driving and we get there few minutes faster on average (except for MK).
If you don't like to drive, use the busses. If you don't mind driving, I still suggest you drive everywhere except MK.
Oh yes, one more thing. Avoid the DTD busses like the plauge. As the night gets later, the busses get very, very crowded. I waited for over an hour once at DTD as full busses drove right by our bus stop. Ever since then, we ALWAYS drive to DTD. I know other posters have had different experiences, but I don't want to risk having this happen to me again, so I wont take the chance on DTD busses.