We take the route through the Virginias and we love it. Our first time driving (we have now driven twice, third time coming up soon), there was a storm coming in (we knew about it), but we left anyway at around 4 or 4:30 a.m. on a Saturday morning in late January 2005. In retrospect we should have left the night before so we could have missed it. The snow started at the NY/PA border and we made it to Pittsburgh before deciding to pull off - and it was only 10:30 a.m. We stayed in a hotel there until the next morning when and we drove straight through to Florida. After Beckley, the roads were totally clear the day after the storm. Every other time we have driven, we have had no trouble, including on the way back during that same trip in February.
My parents drive this route every year in early January and late February/early March, and they have never encountered a problem.
I think the key is to check the weather diligently before you are leaving and if there is going to be bad weather on that route, choose I75. The other option is to do what we did and just be prepared to pull off for bad weather, such as snow, ice or fog.
I75 can have really bad fog areas as well, so it is not guaranteed to be better, plus it has a mountainous area through Tennessee as well.
We bought a new Rand McNally road map this year which shows every state separately so if there is a bad accident or bad weather, we can see our options to go around.