We usually use a rental car. Just makes things easier and puts us on our own schedule. My DH and I went down in January and rented an SUV for $65 for the 6 days we were there. So worth it.
When I went with just my DD last August on a surprise last minute trip, we used Magical Express and Disney Transportation, 1 - to save $$ and 2 - because I didn't want to drive around down there by myself.
Gail
80 & 91 WDW OffSite; 10/95 DL Honeymoon; 4/00 & 5/01 DL Off Site; 12/02 WDW - ASMo;
10/03 WDW - CSR; 5/05 WDW - ASMo; 2/07 WDW - SSR; 8/07 WDW - Pop - Me & DD;
1/08 WDW - CBR - DH & Me; 8/09 WDW - THV & SSR; 08/11 WDW - Pop w/Free Dining