Depends on which way you come into Knoxville and how soon you wish to be there. 5 hours before kickoff and any route should be fine.. 23B is a good spot for parking IMO.
Time wise, Vol Walk is 2:15 before kickoff.
You can come in Neyland Drive to Lake Loudon. I used that lot once and entered and exited that way. I was staying up in Pigeon Forge area at the time. In general I always got to parking spots 4-5 hours before kickoff to tailgate for a while. At times earlier depedning on who is with me.
You can come in Cumberland to Volunteer Blvd or Phillip Fulmer Way also..