Redesmere - gotta be up there defo, due to the pure fustration of being hemmed in alot of the time and not being able to move on to fish or whatever...i would'nt quite call catching them piss easy either.
Cole and another of the Shropshire meres, Deer park , yes , can vouch for them, certainly the hardest for me.
Who can say?, waters are hard for so many different reasons, for different anglers styles of fishing, day only fishing, sheer size and lots of natural coupled with low stock, lots of pressure, wise fish, etc etc
They're all hard !!