We found this too - got to Skipton and went straight to Bizzie Lizzies based on prior experience, and were disappointed. The only thing that was above average was the price, but the quality was not a patch on previous years.
The best one by far we have tried in the last few years is the van parked in the carpark behind The Dusty Miller pub in Mytholmroyd. The people running the van have a longterm lease on a couple of spots in the carpark, and the van never moves. Lots of people drive in from Hebden Bridge and Todmorden to get fish and chips from there.
The best ones we have ever had were from Anstruther Fish Bar right on the harbour at Anstruther. They helpfully tell you which of the boats in the harbour caught the fish they are currently cooking. You could probably get there by canal boat but I wouldn't recommend trying to!