We normally rent a car, but have disney take care of our luggage. But only if we can get a really good deal on the car. If you look on hotwire.com you should be able to come up with a rate around $20.00 per day. The last time we paid $12.00 per day. It really depends on what your plans are & how patient you are. We like using the transportation system if you can use one bus or boat. But when you are trying to go to another resort for dinner its really a pain to have to go to DTD, or a park, to switch buses, and then the reverse after dinner. Especially if you get near closing times for the parks or DTD. If you do decide to skip the rental car, plan accordingly. Either don't make any meal reservations at the other resorts, or make them early in the evening so you don't hit park closing on your trip back to your resort.
Matthew