I think it really depends where you stay. We just stayed at BCV, and would never had used a car at that resort. Quick walk to EPCOT, boat to DHS, and easy bus rides to MK and AK. Plus we wouldn't ever drive to MK with the extra ferry or monorail ride from TTC.
Staying at more of the remote hotels, I think a car would be easier. We stayed at AKL when dd was 18 months and had a car. It was nice having a car at that resort. I'm sure the values would be similar.
That being said, since we fly, and now have three dds that need carseats, we will be using ME until at least one or two of them are out of the carseats. We really don't want to have to lug those things around the airport, wait for a rental car, buckle the seats into the rental car, and deal with having to drive around. The other thing I hate is buckling tired, crabby kids into hot cars after the parks. It's so nice to walk onto an air conditioned bus with no buckling of three kids. The stroller and bags are not that big of a deal. I say this having just come back from a trip with a 5.5yo, 3.5yo and a 5 m old. We had a lot of stuff, and a baby that can't yet sit up. It will be buses for us for a while.