In the UK it has to be Essex, because there is nothing there, no squats, no chance of a ride, no decent places to go, no decent people to be with, it's just a consumer wilderness like the set of some horrific distopian sci-fi nightmare, full of fake-tanned women and preening idiot men cooing and trilling over their recent purchases and soaking up more TV than you would have thought humanly possible. The place should be cleansed by fire and turned into an ornamental garden.
Having said that, Brighton is pretty fucking awful and a very close second, but for different reasons. I mainly hate it because it is full of "travellers" who went to £16,000 a term boarding schools and live in squats while always having their trust-fund and daddy's little place in the country to fall back on if things get too real. It's a mecca for priveleged rich kids wanting to slum it while spending absurd sums of money on juggling balls and carved celtic rune-shoes. They also helped elect the country's first Green candidate who has spent her entire career trying to distance herself from the environmental movement.
Honestly, don't go to Brighton, ever. Just sit in a ditch eating dog-shit and glass, you'll have a much better time.