Hi, mipato,
You may have already taken your trip...what route did you choose? "Best" is a tough one. For some people, best might mean quickest; for others with kids, it might mean "with several interesting stops along the way."
Obviously, you could drive the highways and check out some big cities along that route: Indianapolis, Louisville, Nashville, Atlanta, Tampa. Which means you could visit the Indianapolis 500 Speedway, Churchill Downs, the Country Music Hall of Fame, The Georgia Aquarium and/or Busch Gardens.
There are lots of great ideas in the AAA TripTik. It's got great road information, discounts on hotels and restaurants, activity suggestions, gas pricing and much more.
I hope you have (or had) a great trip!