There are a lot of good comments on here, but I would rent a car if the additional cost wasn't burdensome. It gives you options.
If you haven't been to WDW before, realize that it does take awhile to travel between parks and resorts. With a car, you can do it on your own time, but with a bus, you are at the mercy of Disney's schedule. On our last trip in March, we vowed never again to not get a car, even though we stay onsite. Time is money, and we didn't want to waste our precious vacation time waiting for buses. Perhaps we had a few bad experiences with the buses on that trip, but some of the magic was lost when we saw multiple buses pass us by that were going to other resorts and ours took up to 50 minutes.
Oh no! What resort were you staying at? We stayed onsite for the first time, last year at OKW (which we loved!) and had no problems with the buses what so ever. Our rental car was only used back and forth to airport. Boy what a waste of money. So this year we decided to stay onsite again (this time SSR) with no car. Hoping to have the same good experience with the buses.
