I prefer the drive - hate all the BS involved in flying now-a-days.
If you are civil war buffs, a stop a Stone Mountain just north of Atlanta is worthwhile. Also the Chichamauga Battlefield and the Lookout Mountain Battlefield in Chattanooga, as well as a ride on the Incline Railway, is worthwhile.
If you are taking your time, an overnight at the Chattanooga Choo-Choo might be interesting as well as a visit to the Chattanooga Aquarium.
The drive along I-24 from Chattanooga to Nashville can be beautiful, especially as you cross Mounteagle Mountain.
In Nashville, there is a dinner boat river cruise that many have said if quite good. I have not gone on it.