We drive to WDW (that's how we are able to visit so frequently) - so we have our minivan. We did use Disney bus transportation on our first trip to WDW - and it was tough with small kids. The buses were crowded, the waits were long (it was Spring Break time, but I imagine summer season is comparable), and people were less than considerate. Anyway, we feel it is more comfortable, convenient, and safer (seatbelts, no standing on buses) for the kids to drive to the parks - but everyone has their own opinion on this topic. If you are willing to drive, I don't think a weeks' car rental is much more than a car service or Mears to take you to and from the airport (try mousesavers.com for good car rental ideas - L&M rental is at MCO and has some great rates).