This is strictly opinion...but I would say friday. There is the car show and later on in the day the test and tune starts back up so you get to see all the show cars plus racing. Trophy presentation later in the eve also. As far as buying a car I would say early in the week, if there is something there thats a good buy it wont last long...of course alot of cars for sale dont show up till thursday or friday so its basically just a coin toss on that aspect of it. Hope this helps.