When are you traveling? How many days do you have to get from IL to Charlotte? I traveled this route several times. Well, not from Effingham but from Mount Vernon. I-64 is a better option than I-40 through TN. Take I-64 through Louisville, KY to Lexington, KY. From there I-75 to Knoxville, TN to I-40 which takes you through the mountains to NC and almost to Asheville. Take I-26 east to Columbus, NC and change to route 74. Once you get to Kings Mountain or Gastonia in SC take I-85 North. From there it is only a short distance to Charlotte, NC. Get your gas in TN and then in SC. The least expensive gas is in SC. If you can, forget about buying gas in NC. I'm not sure what you mean by <best, especially though the mountains>. Do you rather avoid mountains or do you want to go through scenic mountains?