As an a'fish'onado (gerrit?) of Fish and chips I prefer Haddock but only because it tends to keep it's flavour and texture longer than Cod. That said, ultra fresh flaky Cod-not counting the tail end- is, for me, superior It is less consistent in chippys though. The BIG question is what is it fried in? It HAS to be beef-dripping nothing else!
Haddock, that's what they eat at the coast because of the cod worms. Barnsley seems to prefer cod though.