We use them from Chattanooga and have always had a good experience.
If you book online there is about a $15 convenience fee per ticket so we go to the airport to save that.
You can do a one way rental from there to Disney and drop off the car. National/
Alamo are at the Swan/Dolphin and
Budget is at the Doubletree in Downtown Disney. The easiest is to use the Swan/Dolphin one and walk to Hollywood Studios and get a bus to your resort. Reserve another car when you leave and take a bus to the Studios, walk to the Swan and get your car. For a short stay it is easier to just keep the car.
We take 417 the Greenway. It is about 45 minutes and 6-7 dollars in tolls. I have seen a few speed traps along there within 20 minutes of the airport so watch your speed.