We had great experiences with the busses all except once, when we were going from MGM to Epcot on our last day... and we could have taken the boat, we just wanted to arrive in Future World rather than World Showcase that time. The Pop Century bus system in January was great. The only time I would recommend taking a car is if you're trying to go to another resort, or if you're going to a waterpark (you can leave things in your car and forgo the locker without having to ride the bus back wet). We fly to disney and have never considered getting a rental car, at least not unless some day we decide to venture offsite. Even though it might take a bit longer, it's really relaxing to not have to drive the whole time you're there... and the bus drivers are some of the most interesting CMs to talk to! I'd say having the option of a car to get to an early breakfast ADR might be nice, but unless you have to leave immediately instead of waiting 5 mins for a bus, give them a chance.