Just wanted to chime in here!
We rented a car in Raleigh and drove to WDW this summer! We used Alamo. To drop it off, we just drove into the driveway at the Dolphin, a valet came over and took all our info, and sent us in to the Alamo desk at the Dolphin. The clerk could not have been more nice, and we were on our way to Epcot after a 1 minute transaction. I can not recommend this more highly. You can also rent or drop off a car at some of the Downtown Disney hotels. I thought we would just drop it off at the Car Care Ctr, but it was so great to be able to use the Disney Transportation right at the Dolphin to go to our next stop. I would use Alamo at the Dolphin if you can. We got a very competitive rate with Alamo too. Good Luck!