Usually we drive so we already have a car when we get there. The time we flew, we used Alamo and they really went above and beyond. Near the end of our first trip, a hurricane was bearing down. WDW and the airports, having been slammed by a hurricane a few weeks before, were already closing up shop. The parks wouldn't open that Saturday and possibly that Sunday, which was our checkout day. Alamo was OK with us driving out of Orlando with their car. We left Saturday morning before the storm hit. We drove all the way to Philly airport where family picked us up. Alamo didn't even charge us for not refilling the tank because of the circumstances.
I can't say good or bad about Dollar, but I will choose Alamo every chance I get.