Best day for what?
Wed is best day for a-jumble, then although this is what I have been told, not all the dancing girls are set up until Thursday
Saturday is just too crowded although the evening fairground atmosphere might be regarded as best, but it is very crowded there although all showmans engines will be running, other evenings it might just some of them or they pack up earlier. Also getting in will be the worst day for traffic.
Sunday is a bit dreary lots of gaps where traders have cleared off.
If I was not already there with an exhibit & came for one day, I would choose Thurs or Friday.