We have cruised three times with
DCL. We used their transfers the first time and rental cars both of the other times.
I would never use the transfer by bus again. Yes, they did show Mulan during the ride and I guess if this wasn't available in my home 24-7 there might be some appeal. I think this is a very expensive, boring way to go. The magic begins when you enter the terminal. Get there early. There are characters, videos, and this is the time that we have had fun getting to know other cruisers.
We usually drive our bags to the port, then drop off the car so we don't have the hassle of switching the luggage except at the airport. The
avis shuttle is very fast and easy.
When we did land/sea, we found it most economical to get a rental for the whole trip and just leave it at the Radisson while we were away (this was actually cheaper than 2 separate rentals). We took the hotel's shuttle from the port and with early seating, this was so efficient that we were at WDW the day we disembarked by 9am!