The towns of Hardeeville,Ridgeland and Yemassee are good for watching trains
on the CSX Charleston sub in the Hilton Head Island Area.
I know they're passing very often. There's a lot train traffic there.
In Georgia,the Savannah Amtrak Station could be a good spot for watching CSX and Amtrak trains included
Jesup and Folkston in the south of the Georgia close to the state of Florida border.