You do not want to be on 20 any more than you absolutely have to. I recommend taking 20 south through Athens to get to 77N, When you get to exit 48 you have a choice, you can continue on 77N or take 19 to 79. It is more scenic than 77, but you'll want to have a full tank before you get on it. Or you can stay on 77 to Charleston and get on 79 right away. Staying on the interstates is faster, but not as scenic. Do not get off on 33, it is good until you get to Elkins, then it gets rough. Rather, continue north to 50 to Brookside, then 24/219/32 to Canaan Valley.