We usually take the busses, but for our upcoming trip, I think we are going to rent a van. We will be @ Disney in September during the free dining staying at POP and I know that the place is going to be a zoo.
I really do not like POPs bus service, every bus is ALWAYS packed!!! At last years
MNSSHP, we were staying at CSR, but we looked over to the POP bus line and it was through all the bars and going out past the All Stars line, and this was already past midnight!!!

The people in that line easily has over an hour wait to get back to POP.
I just think there is more convenience in driving to the parks. Mainly, because you dont have to waste a good 30-45 min of your morning waiting for a bus, and when you want to go back to the resort you can just hop in your car and go.
Now, I dont know about the All Stars bus service as I have never stayed there, but they do share busses among all 3 all star resorts, so IMO I dont see much of a difference between their service and POPs.