Thursday is not too bad – not just the Moving motor show. Most of the classic cars, racers etc will be in the paddock and there’s way less people wandering around. The BMX/MX stuff will be happening as well.
This year they are running the supercars up the hill on the Thursday as well and there is usually some action on the Rally stage as well.
If you can only do one day I’d do Friday, but if you’ve got a crazy weekend that weekend then go Thursday.