We just did WDW after getting off the Destiny a couple of weeks ago. I looked at all the options - even flying, Southwest had a $49 flight from FLL to MCO but it left a bit too early. I was surprised that
DCL did have a bus taking people to WDW after the cruise. However, there is only one bus and I believe it leaves at 9:30am. I would have thought the Brightline would have gotten us there quicker, but it's not the case - especially since you have to take it to MCO and then get to WDW from the airport. Plus, it was more expensive. We settled upon doing express walk-off (got off ship before 7:30am) and going back to the airport and getting a rental car and driving to WDW - which took just about 3 hours from the time we left the airport.
We booked our rental via the WDW Car Care Center website:
https://partners.rentalcar.com/wdw/
Got a one-way rental from FLL and returning to the Car Care Center with Alamo. It was about $65 for a compact SUV (they let us choose from the mid-size SUV section when picking up). Returning the vehicle at the car care center was super quick and easy and they shuttle you where ever you need to go. We were in a shuttle on our way to our resort within 10 minutes of arriving.
There's no doubt in my mind this was the absolute fastest way to get to WDW and into the parks - if that is what you're looking to do. If you're not going to the parks that day, and therefore not in a great hurry, you can choose another method like the DCL bus or Brightline and avoid driving.