If we have a vehicle, we always drive. The Pop-MK-C commute time is a bit unfair, because if you drive, you only get as far as the TTC, then bus or Monorail to MK, then walk to the Contemporary (not a long walk, but a walk none the less). Obviously, driving straight from Pop to the Contemorary eliminates 2 transfers and a walk.
Our #1 reason for taking the car is comfort-everyone can have a seat, no one gets stuck carrying anything their lap, and we can blast the AC on a hot day. The parking lots are very managable, and parking is free if you stay onsite. If you will be dining at multiple resorts, I can't think of an exception (but I'm sure someone can!!) where you would be faster to bus it-you'd have to bus from Pop to a central locaction, like a Park or DTD, and then bus it to the other hotel, or bus it to a Park and walk/take a boat etc.
I have taken the buses, most often when our group splits up. I have never had a problem taking a bus TO a park, with the exception of a stay at the All-Star resorts, because they frequently share buses at less busy times. The buses are clean, comfortable, and safe, and the bus drivers are, if not chatty, polite and helpful. That said, leaving a park at close and waiting with hundreds of your closest friends and hotel neighbors for a bus can make the happiest person in the world cranky-and forget adding tired kids, cranky spouses and heavy bags to the list.
The buses run as effeciently as possible, but the pure fact is, if there are 400 people trying to get from MK to Pop, someone is going to have to wait for a bus, or two or three or four...you get the idea. And speaking from experience, in particular, the bus from Pop to DTD feels like it drives, roughly, from Pop Century, to Daytona and then to DTD. DTD is two turns away from Pop-no more than 10 minutes. I believe the conventional wisdom is that with exception of MK, it is faster to drive than ride, and because of the bus stop situation at MK, it is faster to ride than drive.
Ress