I-81 and I-77 through PA and VA

Depending on the weather conditions, the decent into Fancy Gap on I-77 can have some pretty dense fog. They have digital speed limit signs that they sometimes adjust down for that reason. I think the fog can be more of a concern than the grade itself; there are occasionally some pretty massive pile-ups from people outdriving their sight lines.

As with anything, if you pay attention and drive appropriately for the conditions it's a very reasonable route and I think about the best way to go all told.