We have been down the Blue Ridge/Skyline drive twice and really enjoyed it. Lots to see and do. The Great Smoky NP is at the southern end.
We went up the Natchez Trace, mostly, last year and it was not as impressive. I made an error tho and assumed that it started at Natchez and missed the south leg which starts at Jeckson IIRC. So maybe that is more interesting.
There is a lot of free camping on the Trace tho,