Any of the rental companies near DTD or on property would work for you. They have shuttles that will pick you up at your resort. From SSR, we were picked up by a shuttle once and another time we took the boat to DTD and I walked to the rental company located in a hotel lobby.
If you aren't sure which companies have rental cars near or on WDW property, use Lake Buena Vista, FL, to search for cars on the rental company website.