I don't know if I have a favorite, especially since I haven't been to each one, but I love a lot of things about the south.
The rolling hills of Tennessee and the Great Smoky Mountains are just beautiful with all the wonderful colors of leaves and undulating hills. Nashville is a charming city and is much much more than honky tonk.
Along the other side of the Smokies, western NC is also beautiful. Asheville is a sweet little town surrounded mountains.
The whole Blue Ridge Mountain area is just really lovely on up in to Shenandoah and southwestern VA.
Richmond is a great little city that often gets overlooked but has beautiful avenues and great street art almost everywhere.
Coastal NC is nice and relaxing.
Charleston SC is a great food and cultural city.
Myrtle Beach is probably trashy but I spent many summers there as a kid and I have good memories of it. It's probably fine for a family vacation. Maybe like an Ocean City of the south.
The pace of life in GA is just slower but enjoyable. Athens is another good little college town. Atlanta is also a great city.
I really enjoyed Bay St. Louis in Mississippi, when I was there it was described to me as a "spot of blue in a sea of red". It was devastated by Katrina but the people who are still there are holding on and it's a lovely little artisan town.
The things that are nice about the south are driving along country roads and through small towns, stopping for some boiled peanuts and antique stores. Most people will go out of their way to say hi how's it going like it's just a natural way of life there.
Florida may be mostly shitty, but the keys are nice, however I never really get a major feel for southern culture in FL.
WV is a surprisingly fun and beautiful state to drive through. John Denver wasn't mistaken singing the praises of that state. Kentucky is also wonderfully charming and I found Lexington to be a welcoming place for a young urbanite.
Never been to TX, LA, OK, AR, only driven through AL. Even though they technically are on that list, MD and DE aren't really southern. Native Marylander here.