I assume you mean I40 to I81. I64/77 thru WV has a lot of mountains and it's a toll road. It's a beautiful drive and one of my favorite pieces of interstate but it is right thru the heart of "The Mountain State". I64 from Beckley to Lexington, VA has very low traffic volume. I81 has extremely high traffic volume, most of it 18 wheelers. It's one of the busiest interstate corridors in the country.
If you don't mind mountains I'd take I64 thru WV for the scenery and less traffic. If you want to avoid mountains, go I40.
