DO NOT attempt back roads in this neck of the woods unless you want to extend your drive time by lots and lots and lots!!!!
I speak from lots of experience
Now, if you have nowhere to be, the towns along the way are quite lovely!
Also, US1 from Jacksonville south takes forever. I-95 is much, much quicker.
If you wanted to detour in Savannah, the detour from I-75 via I-16 is a reasonable hike, and it's not that much different to take I-95 vs. I-75 as far as traffic is concerned.