We had always used Disney transportation when travelling to the world, even on Connor's first trip at 20 months. It was a bit of a pain with his stroller and all his stuff, but we were travelling with my parents and my sister, so there was always lots of spare hands to help. On our trip in April this year, we had to rent a car because we were joining the rest of my family in Daytona after a few days in the World and they didn't have room in their car for all of us. I think it spoiled us. We'll probably get a car from now on!
I really liked the flexibility of having a car, especially for getting water/snacks at the grocery store, and shopping off site (Disney outlet! and
Walmart/Target). I also really liked going at our pace and not having to factor in bus wait times. Connor is a really busy boy and doesn't have a lot of patience to wait in line so the less waiting the better.
We also really like eating at resorts (Boma, Chef Mickey's!) and it is soooo much easier to drive than take the bus.
The only time we take the bus is when we are heading to the MK for our nighttime activities and planning to stay till close. I read a tip somewhere that closing time is busier to get back to the parking lot to a car and then your resort than it is to take the bus, even if it's packed or you have to wait more than one bus. We have found this to be true, and the munchkins will usually sleep on the bus ride back anyways. Plus Connor loves busses, so we have to have at least one ride on a Mickey bus each trip!!
This last trip, just dh and I, we stayed at OKW, renting points from a member. I was really glad we had a car because our studio was in a building far from the main bldg and pool area. It would have been a pain to have to wait for a bus just to get up to the pool/shops.
Next 2 trips we will need the rental car to travel to the beach/port, so I think it will be some time before we rely solely on Disney transport again.