If there is another thread that answers this please point me to it.
I am trying to decide which is best for for my extended family of 7 (5 adults, 5 year old and 18 months). We will not be leaving the property.
I am looking for suggestions as to how do a cost comparison and other intangibles between these two (or possible other) means of transportation.
It's really going to come down to your itinerary, flexibility, comfort level and budget on your trip.
For a rental with a party of 7, you are going to need a minivan or large SUV (with 3rd row seating) OR 2 FS car rentals, both of which are going to increase the cost of the rental significantly. If your budget allows for the expense, this gives you the most flexibility for your transportation needs both onsite and offsite. I also suggest bringing car seats from home. You can rent them but they are not the best and costs add up quickly.
Uber can be a good alternative but with a group of 7, you are looking at 2 vehicles per trip since even Uber XL usually has seating for 7 max (including the driver). Essentially, each trip will cost you double and may be a bit of a logistics nightmare coordinating both Uber vehicles at the same time (or maybe not, I've never need to try this since it's usually just me and the DW) Car seats can be requested with Uber but I believe 1 per vehicle and has to be requested in advance as not all drivers carry car seats.
Disney transportation will be your cheapest option. Not the quickest or most convenient but works very well for moving huge amounts of people from the resorts to the parks and back daily. Not really a good option if you want to go to other resorts (say for an ADR) or venture outside the Disney bubble, but Uber works well in a case like this as a supplement to Disney transportation.
FYI:No car seats needed on the buses (+ or - ???)
Afterthought: If you are using Disney transportation and some of your party are early risers who want to do Rope Drop, while others would prefer to sleep in and go a little later, the buses run all day so you don't have to "rally the troops" at the bus stop at dawn. If you have one rental, you will have to coordinate everyone together. 2 rentals would allow 2 seperate groups to work on their own schedules. JMHO