For me, the best has to be either Forest or Blackpool; but to prevent accusations of being biased I'm gonna say Blackpool. There's not many away days where you can start off in a Sports Bar having a pint with your mates, before then heading into an Amusements Arcade, followed by pissing around on the beach making sand knobs and then going on the Waltzers on the pier. Oh, and then you have to go to the football
Worst i've been to is probably the ground we played at in Portugal this summer. It's half an hour walk from the Strip, and about 20 minute walk from the Old Town where we started; despite being told it's only 5 mins away. Plus it's up hill in 35'c in July. Absolutely knackered. Nothing around it neither apart from houses as it's far away from all the holiday resorts and the beach. Closest thing to it was a KFC on the main road 10 minutes away.
In England i'd say Middlesbrough. In the middle of an industrial dump.